hanging plug??

K, there's a plug hanging from my car underneath...it's right behind the oil pan. I can see where it plugs in. Any idea what it is? I can't get her in the air until tommorrow. (I'm pregnant) Hmm...car hasn't started in 4 days. I hope this is the problem:) Any help is appreciated.

Probably the block heater... Must've fallen down in the engine compartment at some point. :)