Random Analogies

"Quaternion is like the plague: it's fun at first but then all your descendants hate your guts for it. They're like complex numbers only they have three orthogonal imaginary axes instead of just one, and the group of unit quaternions is isomorphic to the R3 rotation group for whatever reason (quaternion multiplication = rotation composition, quaternion conjugation = rotation inversion, etc)."

"A solid is like the rock we used: definite shape, volume and mass. It was hard in the hand. A liquid is like water: no definite shape, definite volume and mass. Flour behaves much like water in some ways but not in others."

"The body's cerebrospinal fluid is like a hydraulic pump. Subtle pulses of this fluid circulate around the brain and spinal cord, nourishing all tissues that make up the central nervous system. "