Never eat raspberries

Grandpa: Well, you could skip town. But then you'd have to live the rest of your life in fear, always looking over your shoulder, waiting for... that day. You try reasoning with him? Oh, a moron, eh? Well Arnold, I wish I knew what to tell you. In eighty years I think I've only learned one thing for sure.

Arnold: What's that?

Grandpa: Never eat raspberries.
Grandpa holds his stomach

Grandpa: Gotta go!
Grandpa runs to the bathroom