[snackbroken]

Ants exhibit rather complex first-aid behavior in response to wounded nest-mates (amputating mangled limbs, coating wounds in anti-microbial secretions, carrying the victim off to safety, feeding the wounded ant while it recuperates) so it shouldn't be all that surprising that the comparatively huge brains of mice are capable of similar pro-social behaviors. The inner emotional lives of mice are as you say likely to be much richer than the average person gives them credit for.

[OgsyedIE]

If the lives of nematodes are rich enough to experience a PTSD-analogue, young honeybees can play with balls and fruit flies enclosed in a glass box can vary their flying behavior in a way that is inconsistent with confusion and consistent with boredom, who knows where the limit is. I once saw a paper that argued the middle germ layer of placozoans might support a rudimentary neural network encoded in glutamate-GABA gradients instead of neurons (since they don't have neurons) that could carry out aversion behavior coordination across the entire placozoan body.