Grow pumpkin seeds inside a pumpkin!
Adam Rifkin stashed this in Pumpkins!
This pumpkin project involves cutting open a small pumpkin and adding soil and water to see if the seeds would grow.
They only opened up the pumpkin, left all the "guts" and seeds as they were (except the few that came out with the lid), and
They added a little soil and water and watched the seeds (which were already inside the pumpkin) grow. A few weeks went by and you see the sprout above.
3 months later the pumpkin plant sprouted:
3 months after that the pumpkin plant flowered:
Full writeup here: http://www.growinginprek.com/pumpkins.htm
They are not sure how well a big pumpkin would do.