We have seen the deadliness of bows and arrows first hand, we should try to craft some of our own, maybe using blue rock tips for some of them. More accurate and longer ranged than most slings with less training required to become competent. Start with non blue rock tipped ones first.
Also, let the people have the rest they desire.
(3)One thing you found particularly interesting during the hunt that almost lost you your hand was how your attackers were able to kill two of your people before you even had a chance to react to what was going on. One second you were ready to kill another beast, the next two of your man had small-spears sticking out of them and you were under attack. The idea of being able to strike before someone had a chance to realise what was going on interests your massively, as such an ability would surely be a huge boon to your military. You've even already made a few similar looking small-spears that seem like they should definitely be able to penetrate something at high speeds, you're just not sure what you need to actually get the small-spear moving at that speed. You never actually saw what your attackers used to throw those small-spears at you at such high speeds, you barely even remember what the small-spears looked like you were so focused on fighting at the time, but you remember that it made a sound. Thip? Thwip? Something like that. Therefore, you should just need to go around trying to combine things together until you find something that makes that sound. That, or you could try and figure out your own way of throwing the small-spears quickly. Yeah, that sounds better, you're pretty sure you can figure out something. Eventually.
Oh, and you gave you people a few moons of rest. It turns out that some of them have been getting a bit upset about the constant work they have to deal with, and some even believe you're trying too hard when they really don't need any of these new things at all. Hey, you're pretty sure that there are more of those people now. That's... worrying. Very worrying, actually. You should probably deal with that soon.
What if we throw a thunder-rock at another thunder-rock?
(4)Hmmm. Hmmmmmmm. If thunder-rocks get angry when something touches them and respond to this by invading that thing, you're not sure what would happen if you did this. They could cancel each other out, maybe cause some sort of unending loop... or they could cause an earth shaking explosion. Being an intelligent man who clearly respects the spirits a lot, you don't want to do this, as you're pretty confident that this would end explosively.
Hey, wait a minute, maybe that's what happened to the shamans! The evil shamans forced two thunder-rocks together! That would also explain why the red area of the mountain is also the site of a sizeable crater that wasn't there before. Yeah, that definitely makes sense.
How about testing how strong the reaction is over time: use the same one thunder rock over and over to see if the spirit inside retains its strength, lashes out ever more violently, or if it weakens. If it weakens, the next investigation is to give it a break to see whether it recovers. If more violently, let it rest to learn at what speed its anger subsides. We know that the thunder rocks had a rest after the death of the old shamans, so resting them should be effective. This might be what the previous shamans were working on, be extra careful.
We should also investigate the effects on 'victims' over longer intervals of time. Perform the 'remembering the previous boulder' experiment with a long wait between the two interactions – say, a half or even full turn of the moon – to test the duration of the spirits' wrath. Also insist that the apprentices who have the strongest symptoms in their hands take a break; humans and boulders have a different nature and perhaps the spirits are more forgiving of flesh than mineral.
(5)You spend a few full turns of the moon studying these rocks closely with various tests. From what you've figured out, the thunder-rock spirits are actually very good at remembering previous offenders - one of them completely shattered a half broken rock that was gently nudged against it after a full moon-turn had passed. Another experiment you had was getting a group of people to just constantly throw normal rocks of varying sizes at a thunder-rock over a 10 moon period. You could not see an immediate result during the experiment, but it did perhaps seem slightly dimmer than it was before the experiment. It also did not regain it's previous brightness, assuming it really was dimmer than before.
The people touching the rocks also found that the tingling remained after a few full moon-turns had passed. After taking a closer look at those people and how they treated the rocks, you found that the ones who moved the rocks around the most reported the tingling sensation the soonest, and the ones who used the rock the longest reported a more noticeable tingling feeling, with one very active shaman reporting that it almost seemed to send a dull throbbing pain of sorts through his hand when he touched it, though this pain dissipated when his hand left the rock. This means two things. Firstly, being very careful with the thunder-rocks makes you far less likely to suffer injury, but it is not perfect and even very light movements are remembered by the spirits and slowly pile up. Secondly, the dull throbbing pain most likely suggests some sort of wave of spirits attacking things they perceive as threats, suggesting that their method of attack is perhaps not quite as simple as simply entering the offending object and exploding it from the inside. Probably.
Regardless, you have made it a rule that anyone who wishes to touch the rocks must wrap a thin length of fibre around their fingers to ensure the safety of their person and their continued ability to use their hands. You really don't want to anger these spirits so much that they actually kill one of your shamans, that would be very bad.
You're also pretty sure you've figured out the thunder-rock's basic rules at this point. It's spirits are easy to anger, and respond to touch by attacking the object touching them, regardless of that object's intent. They remember an object that has previously touched them for at least a full turn of the moon. If treated gently and slowly the spirits are slower to anger but will still eventually begin hurting the thing holding them, no matter what. They are shiny and blue. They dim incredibly slightly with every use, suggesting that not all of the spirits are able to make it back into a thunder-rock after an attack.
(3) You're pretty confident that you can't get much more advanced with your ropes at this point - they use the best fibre for the job, are constructed the best way they can be and they're very capable of holding your weight. You're not entirely sure what you'll use them for, as you can't quite remember why you chose to order their construction, but you definitely have a lot of rope now.
It has been 3 full turns of the moon since you first started thinking of better small-spears, and progress on most things has begun to grind to a halt as the Cold Moons are coming as the great spirits of cold begin to overwhelm those of heat. It has become something of a tradition for your people to spend the colder parts of the cycle deeper in the cave, where it becomes much warmer and more comfortable during this time. This part of the cycle is generally spent simply sleeping and occasionally waking up to eat some plants and drink in their delicious juices. You have pushed the limits of how much work you can get out of your people, and many are beginning to get upset. You have had them work an unnecessary amount throughout the entire year and, after a few moons of rest, you have had them work and experiment 2 moon-turns into the cold years. Some are beginning to believe that you are perhaps not the person best fit for the position of chief after all...
What are you going to do? Immediate issues of importance are that the cold years are here and your people are angry with you for, as they see it, severely overworking them. As far as they're concerned they have so much already, so why should they waste time on new things that require more effort for less gain than simply living in the cave?
Note:The seasons of this world are not directly equivalent in time or severity to the seasons of our own world. They have simply been given the names of three of our seasons because those are the most fitting names for those particular times. 'Spring' lasts 4 months, 'Summer' lasts 4 months and 'Winter' lasts 9 months. Just thought you ought to know. :p