Regard a Mere Mad Rager - S2-E19
Trivia: Even though simply opening the door is the solution, the math problem given yields an imaginary number. In the problem "boing" equals -1 and "flarp" equals 2. Then it asks what is the square root of -1 over 2. It's impossible to get the square root of a negative number since any number times itself yields a positive number.
Trivia: Since episode 10 of season 2, "Nor I, Nigel AKA Leg in Iron", all the episode names (at least to episode 21) are palindromes (a word or phase spelled the same forward or backwards).
