Regarding us: the guy's brain is very much gone, it's called an intellect devourer for a reason. They replace the host's brain entirely (what do you think those little brains-on-legs you fight do?) and control the body.
But you don't know that unless you sadistically rip his brain out of his skull.
If you pass a check you recognise what it is. The voice doesn't sound correct either, for a male elf.
Yeah, I got the Arcana check telling me it was an intellect devourer. It still is the guy's brain though, and he's looking around the whole time, moving his mouth. You pretty much just ignore the guy and go inspect his head. Any reasonable person would first try to speak to him, revive him, or offer to end his suffering. THEN once you realize there's nothing you can do, you could shift around behind him and deal with the brain.
EDIT: Plus you're smiling at the brain as you inspect it, like you're fascinated. It's pretty Hannibal Lecter. Your char should be horrified.
