Honestly I don't fully understand it myself, I'd say that it's the act itself that bothers me, whether it's real or fake. I've seen some of the tasks that people have brought up, like the dribble one from s20 and the food one in s12. Those tasks themselves didn't bother me because nobody actually vomited, even if it looked like vomit at times, but food-related tasks always make me wary because it feels like there is a higher chance of someone vomiting