If you ever need to differentiate between a real or fake pearl, the best way to do it is to rub it against your teeth. A real pearl will feel gritty against your teeth – almost as if you’re rubbing sandpaper against them. A fake or imitation pearl will feel smooth. If you’re unsure, the likelihood is that it’s fake as a real pearl will most definitely grate against your teeth. But how did it get in the fish?