I'm so glad it helped to hear that they seem to know when you're trying to make them feel better
. Though I have anecdotal evidence from cats, rabbits and small birds as well, one of the best stories I have in that regard is from a sugar glider, Hobbes. We hadn't had him very long at the time and while his cage-mate Hurricane has been a sweetheart from the day I got her, Hobbes was unaccustomed to being handled and was both afraid and aggressively unbonded to us (as in hand-greeted-with-lunging-teeth-that-lock-on-like-a-vice-grip unbonded).
One morning (must've been pretty early, since they were still awake), I was watching the gliders in their cage and I noticed Hobbes hunching up and making this weird hissing/clicking noise I'd never heard before. I watched for a couple minutes and it looked to me like he was constipated and trying to poop was causing him pain. So, off to the exotics vet we went. He did NOT want to go and was a real pill about everything - scared and lashing out as he got poked and prodded, the poor thing. After a physical exam, he got x-rayed, briefly sedated and got a scope shoved up his bum. He was diagnosed with enteritis (inflammation of his colon) and sent home with and Metacam (pain killer) and Flagyl (antibiotic... I put my foot down about 'no Baytril' after a previous bad experience giving it to a sugar glider).
Anyway, we get home and I've gotta medicate this sick and angry and terrified glider who would like nothing more than to see my fingers gushing blood. Thankfully, I had some feeding tips (cannula tips), which make getting a 1 ml syringe into a very small mouth infinitely easier. I kept him in his snugly fleece sleeping pouch, using it like a glove... without letting him get loose enough to attack, I had to get the feeding tip into his mouth and squeeze in a couple drops of icky medication before he could jerk away. A very nerve-wracking experience for both of us! I think it goes without saying that he was not a fan of this. At ALL.
24 hours later, I go to repeat this process... but when the tip of the syringe approached his face, his mouth popped wide open! From that day forward, he was never as vicious towards me as he had been before he got sick.
If something with a brain not much bigger than a pea can connect the dots between being force-fed nasty stuff and not feeling miserable any more... and a cat who would normally quite literally try to kill you for attempting to bathe them suddenly tolerates it when they're infested with fleas... then surely our bunnies understand the correlation between being miserable and having a human do unusual things to them.
I actually used to refer to Gaz as our 'Munchausen' bunny because she was prone to gas and the early warning signs of stasis. Sometimes she'd seem a little off and shun a treat like her appetite was reduced and I'd whip out the first aid kit to start trying home remedies... then as soon as I'd dosed her with simethicone and/or probiotics (before they could even have taken effect and without getting pain meds yet) she'd suddenly be back to normal! It seemed as though there were times when she just wanted the attention or to feel like she'd gotten something special from me
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