I discovered Fun Tak in 3rd grade, when my teacher, Mrs. Haczynski, used it to hang things in the classroom. At first, I thought that it was blue Silly Putty, but then I realized that it didn't bounce quite as well (don't tell Mrs. Haczynski I found out!).

Fun Tak is the blue or white goo that you can use to hang up posters instead of using scotch tape. It leaves less residue and it's far less brittle. The name of it when sold generically is mounting putty, not Silly Putty, and it's in the stationery section.