In this video, former Double Dare game show host Marc Summers reveals what was really in Nickelodeon's famous green slime:
Slime gets identified with "Double Dare" a lot, and then again on "What Would You Do?" But it actually started on a show called "You Can't Do That on Television." What happened was, if you said the words, "I don't know," you would get slimed.
You know, it's weird. Slime is hot again. And there's all these recipes online that have nothing to do with what we used as real slime. It started off as vanilla pudding, apple sauce, green food coloring, and a little oatmeal.
However, in a 2016 interview with A.V. Club, Double Dare's set designer Byron Taylor said that oatmeal was not used:
We didn’t use the recipe from You Can’t Do That On Television [for slime], because the oatmeal would dry and harden under the lights, and you literally couldn’t get rid of it. It would turn into plaster. We used a combination of pudding, and I liked applesauce, because it was translucent. You tinted it.
Maybe oatmeal was used or maybe it wasn't, I don't know...