Guy in a Box is correct. I think I remember the others subtitles, in case anyone is interested:
Moai Better Blues: Sam & Max Jump Into A Triangle
Night of the Raving Dead: Sam & Max Meet A Guy Who Really Sucks
Chariot of the Dogs: (I think it just said it was based on the book by Erich von Däniken, but I'll need to go and check again)
What's New, Beelzebub?: Sam & Max Meet The Father Of Lies
Sam's Personal Hell: Based on the recurring nightmare, Sam's Personal Hell
The only mention of the medium I remember is the fake opening in What's New Beelzebub?.