Just like with sex, everyone begins to swap spouses a little differently, too. That's the fun of it, right? And here's how three couples began to swap. In Book One, it was a way to collect money for a local animal shelter, after all, charity does begins at home. In Book Two, a note slipped under the door of a couple on a European river cruise starts it all. For Book Three, things begin when a friend of the husband comes to visit and his wife accidentally sees him in bed naked and, yes, it's big, very big.