So God smote the Egyptians with a bunch of nasty plagues. For example Pharoah once in his bed, awoken with frogs on his head; frogs on his pillow, frogs on his toes, frogs on his shoulders, and frogs on his nose. At least that's what the song says.
He also heard locust––annoying insects hopping around, boils––worse than bad acne, and blood––not the kind that comes each month, but that would have been a better punishment for a guy. I'd have given him cramps, bloating, and moodiness, too. There's many more plagues, but let's keep this short.
Jews aren't supposed to celebrate anyone's hardships, so we spill a drop of wine for each plague, and suffer from less wine. But all is cool. We get four cups at the seder.
Returning to the story, the Jews left Egypt while baking bread. As a result, it didn't have time to rise and we have to eat tasteless, flat stuff that gives us gas. That's the Joyce's Digest version of Passover.