With a Geiger Counter.
Ein stein. - From Big Nate, as told by my kid.
3, duh. (My ex's 9 year old little sister told me this joke, and followed is up with: "and YOU'RE the math guy!" >< Burned.)
Tooth hurty
Because ah, the egg roll.
When it's raining Datsun cogs.
You have to drop the bomb on her twice before she gets it.