I think girls tend to imagine more than guys do for that kind of thing.
That's not to say girls don't watch porn, but I just think girls do tend to use their imagination more.
X
O.o that's not unusual. The thoughts themselves are the stimuli. Carrying porn DVDs in the bathroom is weirder than masturbating in the bathroom with imagination....
Are you a person who is bad at imagination? I don't think so...