Interesting Analogy

dr soc: We need eggs.
me: No we don't, there are still at least a half dozen left.
dr soc: But they're past their expiration date.
me: That doesn't necessarily mean they've gone bad. At least check them before you throw them away and waste the money. I know how to test them, it's fine.
dr soc: How do you check them without breaking them?
me: You submerge them in water. If it sinks it's good, if it floats it's rotten.
dr soc: Like witches?
--pause while I think about that--
me: Yeah!
dr soc: Cool!