It is the rubber sphere, specificaly the big one, use 5 big rubber spheres and then look at the images, they are the ones listed as Latex Ball

Great game, just finished playing and i'd be lying if i said i didn't enjoy it. There were only a few spelling mistakes i saw in the route i took, but nothing that was too hard to "solve". Nice game.

Also, the "Welcome to Izzy's wet dream" line killed me. xD