Approximate group Puns

We divided into groups and the lab was to use the measured volume and diameter of various spheres to find our own approximation of pi. So we had to use marbles and some ball bearings. We get to our station to start measuring when a girl in my group says:

Her:"Hey, where'd the blue marble go?"

Me: "I don't know. It'll be fine though, so don't... lose your marbles"

Her:nearly slaps me

I said it a few times that class, and when some other group dropped a marble down the drain I said it loud enough to get a groan from the whole class.