For a 'Ghostbusters' fan, discovering that Slimer wasn't real was like finding out Santa Claus didn't exist. (OK, not really, but it was still a bit disheartening.) Luckily, a video featuring vintage tests of the Slimer puppet has just appeared on YouTube and shows us exactly how the ghost was brought to life.

The clip starts with some behind-the-scenes footage of Bill Murray speaking with the actress who was inside the Slimer costume, Robin Shelby. The good stuff starts at around the four-minute mark, as we see everyone's favorite ghost in dress rehearsal. It is pretty entertaining -- and a little creepy -- to watch someone control Slimer's every single facial expression through a gigantic remote control.

Hit the jump to check out the entire video.