My kids are scared of the some of the wierdest things.....
My 4 year old is deathly afraid of the Tweeze http://www.buytweeze.com/
and will run screaming from the room, yelling "NO" all the while. I still haven't figured out why, but it is sort of funny when he runs in the bathroom, discovers I am "tweeze-ing" and turns around and runs out.
when they were small, both were scared of the vacuum. The four year old still is, a little bit, but when they were really small they would hide in thier rooms.
Remember those bath tablets that changed the color of the water? When DD was about 3, those scared the crap out of her. I tossed one in while she was in the tub, and then had a wet, slippery 3 year old launch herself out of the tub, screaming, into my arms.
She is now 7 and is STILL scared of toilets, of all things. Not the toilet themselves, but the flush. The automatic flush at Walmart terrifies her and no matter how badly she has to go, she will hold it.