This function allows players to create asymmetrical creatures and vehicles.
For example: a creature with 2 different eyes, or only 1 wing a the right side.
It can be used by simple holding down of the A-key while picking up a part, and holding it until placement..
The asymmetry function was introduced in Patch 5, thus if you have not updated Spore to the latest version the function will not be available.
Originally people would hack the game for this using "ramon NZ's" Spore Editor Hack this was commonly used, but as of Patch 4+, this hack is unable to find the correct memory addresses to use for editing. It has become largely obsolete with the introduction of the asymmetry function, although some functionality must still be hacked in.