Crossword Genius

Their notable behavior is actually involuntary, like fainting (8)

Ross

I believe the answer is:

opossums

(Other definitions for opossums that I've seen before include "American natives" , "Small, furry, Australian marsupials" , "American marsupials" , "Mainly arboreal marsupials" , "animals" .)

I've seen this clue in The New York Times.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.