When I read Boingboing post about silly putty, I didn't expect it to be so much fun, until I've got hold of some myself, that is.
Silly putty is in a solidify liquid state always, it looks and feels like plastic clay, but go ahead, make a great pyramid, in no time it will "melt" down into a pool of goo. Stick it under a ceiling, slowly the silly goo will drip down, like watching slow motion movie. Paste it to a wall, tomorrow you will see a long stretch of dry goo from where you paste down to about 4 feet long.
I play it again, I played for whole day. The only other thing that I am tempted to try, but yet to try is heating it up to see whether it will turn to a real solid.
This goo makes you look silly. (Link)
You can watch my video of how a putty drip from the ceiling in 5 minutes time. (Link)