This one always makes me smile. There's just something intrinsically goofy about two explorers in early 20th-century British safari garb, hunting mathematic entities in the jungle.
When I was taking Physics 122 at BYU in 1998, I drew a large version of this cartoon on the whiteboard in the lab. Amazingly, no one erased that cartoon for weeks! It's not like the T.A.'s couldn't have used the space for scribbling equations, either -- the lab was always packed with students. I take this as a great compliment.