Many years ago I overheard a guy say that with his color-blindness, wasabi looks almost exactly like bean dip. He was at a party once, saw some chips, and a bowl of what he though was bean dip next to it. He took a chip, scooped out a nice dollop of "bean dip", and popped it in his mouth before anyone could react; only to discover that it as definitely not bean dip.
Luckily, he said, he really likes hot things, so while it was quite a surprise, it wasn't as nasty a shock as it could have been.
But yeah, I don't see how you could be confused after the first bite.
Edit: Somewhere else quotes the article as saying that the amount she'd eaten was "about a size of a teaspoon". That sounds similar.