Yep, it was a lesson that cut deep. Which is why I won't let such stuff pass with my own students. One of my coworkers wanted to discourage a kid from using permanent markers and told him he'd give himself ink poisoning. The kid took it to heart and started saying he was allergic to tattoo ink. It was kind of funny at first, but he kept repeating it until it got concerning. I think he was starting to be scared of markers.

I just told him the truth - he's probably not going to get sick, but permanent markers are hard to clean off of things, including skin, and that some of his peers might use them on things they aren't supposed to. He's a smart kid who just wants to understand things and will think through stuff he doesn't understand until they make sense to him, even if it means imagining an allergy to something he sees other people use just fine. It breaks my heart to think that's not the last time some adult will tell him a myth, but hopefully his natural desire to make sense of things will continue to develop into a first-rate bullshit alarm someday.