Watery, milky diarrhea that is discharged during a full moon whilst a werewolf undergoes his transformation.
Werewolf 1: Man, I had a really hard time last night.
Werewolf 2: Why is that? Did you eat a baby?
Werewolf 1: Yes, and it gave me wicked moon juice.
Werewolf 2: Careful of that moon juice, it really sneaks up on you.