Gesundheit lands like he somehow knew it would, and that familiarity combines with the corresponding Tony's easy ability to grin with his jest and makes it all that little bit worse. Ignorance really is bliss. Stephen's never had a problem explaining this to people before - talking magical bullshit to people who'd rather not hear it is half the day job. Is it his favourite pastime here, specifically? No. Does he get through it with minimal wincing? Usually.

Now the corner of his mouth twitches downward as Tony's picks up, and the tiny little spasm at the corner of his eye might well be a flinch. Stephen doesn't go for his own glass until the word purging joins the conversation, then he takes two swift swallows and sets it back down. How is he supposed to break this one gently? He can't. So here goes.

"Purging energy, feeding urges. You can look at it however you like. The long and short of it is that if you don't sate the curse, you'll change. It's only a matter of time."