[As to why Aria didn't immediately shoot, she ran out of action points kicking the door in, roll into the room, raise to her knee and leveling her Gauss to have it aimed, since you wanted it to be a good shot and aim for it's skull preferably or somewhere weak and not a quick snapshot.]
...4...
More Interns swarmed away from 001B, coming closer to the door, screaming and frailing the whole way.
Maximus prepares to punt the grenade..
Aria squeezed her Gauss rifle's trigger, sending a footlong Tungsten-tipped metal spike out through the barrel at four times the speed of sound, the blast wave were visible as scattered items and pens went flying, the gun's recoil dampeners whines and strained to work the arm-ripping recoil into a mere buck-by-a-horse, but Aria's been shooting it a few times now and she wasn't that badly thrown from the shot.
A Fraction of a second later, the spike sped towards 001B, at such range, it was impossible for the serpentine monster to dodge. The spike connects squarely to it's left armored shoulder, under-developed scales shattered and warped as the force of the spike that was meant to shoot at tanks tore into it before exploding out the other side in a brilliant shower of bits of gore and blood, it's left scythe arm was messily blown off and the monster roars in pain.
It prepares to shoot back at Aria..
...3...
there was a dull, metalic 'Clunk!' that was mostly drowned out by the lasting crack of Gauss fire as Maximus's boot connected with the grenade, punting it hard, the grenade flies through the air...
Zander squeezed the trigger of his Gauss pistol, and a moderately sized spike was shot out with a loud, powerful crack that nearly crippled the poor cowboy from sheer recoil alone, his bones rattled as the force of sending something out at 4G kicked back on him, the recoil dampeners were much smaller for the Pistol, and he's not going to be able to feel his arms for hours afterwards..
The spike connects with 001B's right scythe blade a fraction of a second later, it pierced through the hard blade with ease and it's carried force pulled the creature's aim, causing it's spike to go to the lower right than where it had intended.. The venomous spike flies through the air..
...2...
the Interns jumps for the floor, away from the monster and away from the grenade, Frazz also ran away from where it was to an even more safety.
The punted grenade smacked into 001B's face in a faceshot that would've made any football player proud.
001B's venomous spike flew for Aria and found it's mark, the piercing tip penetrated her unarmored leg with ease, it was so fast, her flesh expanded, it's force ripping muscles apart and snapped the bone like it was a pockie stick before a mess of torn flesh and muscles and lingering bone pieces exploded out the back of her leg along with the spike as it kept going, it slams into the floor and pins her with her leg there.
Aria now suffers a -4 to all of her rolls from shock, pain and fright. She's now suffering a level 2 Injury and level 2 fright, being semi-crippled and scared because one of her fucking legs just fucking exploded under her. The pain is almost unbearable.
...1...
Someone is screaming, it might be Aria, it might be the Interns, it might be the others, it didn't matter. The door's clogged and the rest of the Security force couldn't get in and the Interns couldn't get out. The monster is also pissed as all fuck now that it's lost a good chunk of itself under heavy Gauss fire. Everyone is shouting and screaming, it was Chaos.
Then the Grenades exploded. Two High-Explosive grenades of acceptable qualities did it's job, it's beeping became a flatline as it's internal mechanism causes it's payload to explode, superheated air, heat and energy rushed out, blasting nearby remains into smithereans, throwing pens away like deadly projectiles that might've found itself lodged in at least one of the unlucky Interns, a scapel itself was flung and lodged itself just mere inches away from Zander's face,
the force of two grenades sandwiching 001B were devastating, it's growing scales were torn and ripped apart as concussion carried throughout, it's strong muscles were torn asunder and bones were shattered from the sheer explosive force, it was thrown in two directions at once, internal organs raptured and a good deal of it's surface was scorched by !!SCIENCE!! Flame.
When the dust settled, the creature was holding itself up with it's one remaining scythe that has a Gauss spike stuck to it, it was making strangled breathing noises as blood drips from it's orifaces and it's wound that have gotten much worse. 001B will not survive even with the best of modern medicine, but it's still breathing, though barely.
A couple of unlucky Interns that were too close to the blast were thrown away, their backsides scorched and burnt flesh exposed, but they'll live. Probably.
Many eardrums were popped from High-Explosive exploding inside a room, but fortunately none of it were Foxhound's as they were either far away enough from the explosion or took cover.