[[A woman with a ponytail leans back on her office chair, back to her computer, gesturing as she speaks to a little girl in front of her.]]
Girl: Mommy, why is the sky blue?
Mother: Rayleigh scattering! Short wavelengths get scattered 
way
 more (proportional to 1
lambda^4). Blue light dominates because it's so short.
Girl: Oh. So why 
isn't
 the sky violet?
Mother: Well, because, uh... ...hmm.

{{Title text: Feynman recounted another good one upperclassmen would use on freshmen physics students: When you look at words in a mirror, how come they're reversed left to right but not top to bottom? What's special about the horizontal axis?}}