Yeah, I'd be a little miffed. Depending on what it was they snuck down my gullet, they might see my "delicious meal" again! <- (smiley to illustrate my point is stopping at the line of good taste)

I don't mind experimenting with different foods, but not everybody feels that way. I prefer to let people know what I'm serving them, epsecially if it's not what's considered "usual" fare for them, so that they have a choice. I'd like to have that same choice.

I also have dined under the condition of "I don't want to know what this is," but again, that was my choice to make.