There is a bell curve for mercury tolerance, where some individuals are more sensitive than others.

“I guarantee you there's a bell curve right for mercury for mercury tolerance as well I guarantee there's people I could give twice as much mercury and they'd be fine and you're like I don't know that they're very mercury sensitive I don't know what's up with that it's weird right but there are other people you give them a tiniest amount of mercury and they'd be in the ICU immediately and I guarantee you there's a bell curve for that just like there is for every other thing when it comes to human physiology”