proof
Explanation
The Joke
A wild-eyed professor threatens someone: "If you object to my conjecture, I'll put you inside this coil of wires that'll create electrical body currents in your body until you VAPORIZE!" The caption below reads: "Professor Schmidt demonstrates the concept of proof by induction."
The Humor
The comic is a pun on the double meaning of "induction." In mathematics, "proof by induction" is a rigorous logical technique used to prove statements about natural numbers -- you prove a base case and then show that if the statement holds for one case, it holds for the next. In physics, "induction" refers to electromagnetic induction, the process by which a changing magnetic field creates an electric current (as in an induction coil). Professor Schmidt has confused -- or perhaps deliberately conflated -- the two meanings, using a physical induction coil to threaten anyone who challenges his mathematical conjecture. The additional layer of humor is that threatening to vaporize your critics is the exact opposite of how mathematical proof is supposed to work, yet it would certainly be effective at silencing objections.
References
Mathematical induction was formalized by mathematicians including Blaise Pascal and later refined by Giuseppe Peano. Electromagnetic induction was discovered by Michael Faraday in 1831. The comic plays on the shared terminology between these entirely different fields.