Newton is floating in his grave right now

Old Lady on the metro:

"I just think gravity is the most amazing thing. But, I still don't understand how it keeps us, the cars, and everything glued to the Earth while it moves around. I mean, you don't suppose we could be wrong about the Earth not being flat, do you?"

(This was followed by Old Lady nervously laughing, as if moments later she realized how ridiculous her question was.)