I think there are a series of small criss-crossed rails made of steel, that make the seat a pain in teh arse to get it out w/o causing damage to the seat...
I wouldn't pull it out unless I did not plan on putting it back in. I yanked one out of a gutted totaled civic just to see what it was like in there, and I cause irreperable damage to the seat. Good thing no one really cared.