Cat out of the Bag

Who let the cat out of the bag? I think the more important question is who put the cat in the bag in the first place. If there is some maniac running around shoving cats into bags I think it would behoove us all to figure out who this guy is. And how did somewhere along the line letting the cat out of the bag come to mean ruining a surprise? Was there any doubt in anyone's mind what was in the bag? A writhing meowing bag. Hmmm... I wonder what's in it. You know who let the cat out of the bag? A hero that's who! Poor cat.

Not to mention the bag is ruined now.