stock market goes up and down
jell-o - "watch it wiggle, watch it jiggle"
gerbils- um... squeak?
mabey a large running wheel of some kind
also gerbils will dig complex tunnel system if given the space and resources
if you check out the K'nex website you will find they invented the K'nex blocks -
http://www.knex.com/
K'nex slogan is "if you can imagine it you can build it"
i believe that the next task might be a multi-layered tunnel maze that shakes with the scoreing peices at the low levels and you have to bring them to the top (stock market) sounds weird but thats my best guess
i'll keep thinking though