The Secret of the Unicorn: Part 2 - S1-E4
Stupidity: When the Bird brothers are searching the treasure room for Tintin, one of them claims they have found him, and points. The other brother then shoots at him which was turns out to have just been a mirror reflection. The brothers then proceed to find Tintin and start by going straight forward, completely in a different direction than the mirror. If they wanted to find Tintin, wouldn't the more logical thing to do be simply look in the direction the mirror was pointing at? The whole point of a mirror is to reflect what is in front of it, so Tintin would probably have been standing in that direction anyway. (00:37:25)
Chosen answer: It is a pill that makes alcohol taste disgusting.