Those generation x people who grew up trying to finish Super Mario Brothers 1 on their family computers will be familiar with this collectible: the 1UP Mushroom. The 1UP Mushroom is a licensed Nintendo collectible and stands about 6 inch high.
You can actually create an illusion that a mushroom has grown. You just get ordinary garden soil, push the mushroom down on soil and fool your officemates, family or friends (if they're all a bunch of 6 year olds) into thinking you've actually grown an actual 1up mushroom.
The 1up mushroom costs $9.99 at ThinkGeek.com.