In my high school chemistry class, we learned about something called "quantum mechanics". If I recall correctly, it was a theory to describe the way electrons arrange themselves around an atom's nucleus. Each little "cluster" of electrons was called an orbital, and we learned that different atoms had differently-shaped orbitals depending on how many protons and electrons there were.
The (slight) humor, of course, is a pun on the word mechanic. The one thing I'm proud of in this drawing is the lady's facial expression as the mechanic delivers the news. I think it's the best "anxious mother" look I've ever drawn.