At a private show I was doing this weekend I had someone I picked from the audience in a routine. I had earlier verified that she didn't need glasses to see up close. What the routine was isn't important, but it was vital that she got "Tails" on a coin toss. I even picked an old, non-state, quarter for the routine so it would be easy to see and there'd be no confusion. (Some of the state quarters could be anything. 'What is that? A pizza? A Velociraptor?') The coin is flipped, it's "Tails". She looks at it and says it's "Heads"! I was momentarily taken aback... "Um, Heads? Are you sure?" And she said "Yes, that's heads. On a quarter, that's heads."

No problem, really. Since it was an in-home party I just got a bunch of other people to look at it. Yep, Tails. (It sort of derailed the by-play I had scripted. Kind of a surprised and dismayed, "Say what? Tails? Oh..." because I didn't want to confuse things even further.) My main concern was not embarassing her.

I know a lot of older magic books mention that you should check that your spectator knows the card suits if you're doing a card trick and I've never had an adult spectator that didn't know them. (Presumably. Honestly, I rarely do anything with cards anymore!)

I'd never before met anyone born in the US who didn't know heads from tails on a US quarter! If I had been on an actual stage, it could have been a real problem. From now on I will always make sure they know first!

Seems like it's always the things you take for granted that go haywire in performance!

It's amazing the number of things that you take for granted and you end up getting the shock of your life when you end up being thrown a curve ball. I've had it happen a zillion times.

I guess football players don't know heads from tails either since the referee always shows them and says, "This is heads, this is tails" prior to the coin toss.

That's a little different, a lot of times they use coins specially created for that day and the designs aren't what anyone is used to so they have to point it out...gets bad tho when the officials forget which side is which.