There's a ball in my soup

I got a funny email at work today, in French, it was in response to some journal article one of the academics had read. He was saying that either he didn't understand the author's reasoning or as he said in English "there's a ball in the soup" which means that there is something funny going on. But what he actually said was "couille dans le potage" which when you use Google translate says there's a "testicle in the soup". I'm not really sure where this saying comes from, but I thought it was pretty funny.