Ashlin, the entertainer

My daughters are taking after me. They like to make up songs. This is what I remember of Ashlin's as we drove home tonight, rather late, but she was wide awake:

And the cow jumped over
But it did
But it didn't
But it did
But it didn't
But it did
But it didn't

Then she said, "Mommy!"
"Yes, Ashlin."
"I'm going to tell a joke." Rob made a painful sound he thought only I could hear. "Daddy!" Ashlin yells indignently.
"Ooops. busted," Rob says quietly to me, the turns to Ash, "Go ahead Sweetie, tell your joke."
"Why did the cat spill the milk?"
"Why?"
"Because!"
Apparently "because" is now the punchline to an awful lot of jokes. And each time it is said, that is our cue to laugh uproariously. Or at least it used to be. After formerly insisting that we laugh, Ashlin started saying after about half a dozen jokes, "What's so funny?"