At your bathhouse job, you encounter a pair of rainbow serpents, each having two heads, hiding behind a wide pillar. They seem to be bent around the pillar with a head from each serpent visible on each side
You know that for each rainbow serpent, one head will tell the truth and the other will lie. You also know that they are rather ill-tempered, and they'll only allow at most 4 questions between the 2 of them, and that's if you only ask about them. Unfortunately, you have to go ask if they have any problems, and will be expected to fix them if there are any. So you must determine which head is a liar and which is honest, within only 3 questions.
How can you guarantee this, regardless of the answers you get?