Thanks Master Turtle!
How long / how often should you do this? I've been going for 5 minutes at a time, squeeze, squeeze, squeeze. My hands are pretty tired now so I'm gonna probably lay off for a while. It's kind of fun. I'm gonna have badass lemon-squishing strength.
My not-very-scientific advice on new exercises is just to do it as much as you can in one sitting (say three times of as many squeezes as you can, with a minute break between each) and then leave it
two days and see how sore it is (you want to leave it two days because some people can have a delayed soreness from exercise (DOMS)). Then try to work on finding the the right balance between pushing yourself and going too far.
With these sorts of low weight exercises it's not really that dangerous to over-do it (unless you go mental. If it starts to hurt - STOP.) and so feel free to push yourself a bit. With proper weights get proper help or at least use a cage.
Once you can do lemons - buy some grip trainers. They're really cheap and having a strong grip is both great for exercise and just impressive in it's own right. I used to know a policewoman who was tiny (literally
tiny) and she could bring full grown men screaming to their knees with just one hand around their upper arm because her grip was so insane. Like squeeze your bicep now - it probably doesn't hurt at all - imagine how strong your grip would have to be to make you buckle in agony. Scary thought.