I'm fine with choices like that so long as they're things that are reasonably stupid choices. There are times when trap choices are presented in a way that doesn't give the player a way to see the negative outcome coming unless they have a few really esoteric bits of knowledge, or even times when they couldn't have seen the result coming at all, and those tend to feel like just cheap ways to make the player feel dumb. What you describe though is definitely the right way to handle it, though I can see why developers wouldn't want to design too many of those, since most players wouldn't take them and they probably would end up being more work than it's really worth.

Back to our case though, my only issue still is that if players don't know the distinction between a regular animal and a monstrosity, then the choice and outcome verge upon being the cheap sort of trap choice I described.