Because abuse, basically. The paralysis from the drip is enough to keep the yukkuri from hopping around, but not enough to say, cause the same sort of trauma you'd get from searing the foot or spearing it on something. And I wanted to experiment with drawing some slightly different faces.
Apologies for the weird contrast on this and the previous page by the way, I was experimenting with ways to prep a scan of a sketchbook page without inking.
I was thinking lab safety. With frogs, even though they are drugged, they are usually pinned down or secured so sympathetic nervous reaction doesn't cause any hazards. Then again, securing a half-drugged yu with a few bungee cords would probably accomplish the same effect.