Creative answers to "are you twins?"?

I am friends with a pair of twins. They are fraternal, but can pass as identical. Their physical features leave no doubt that they are twins, at least for most people. As many twins are, they are constantly asked if they are twins, sisters, and even if they are related! They're getting tired of answering the more obvious questions, so we are looking for clever come-backs. So far we have, "yes, we are womb-mates," "no, we found each other at summer camp," and "no, our mom just had us at the same time." Does anyone else have clever comebacks to the twin question?