Have you ever looked at something and thought "It looks like it moved". Well you shouldn't worry, it's just a statue made of stone. The only damage it can do to you is when it is actually thrown in your direction.......right?......WRONG!! There is an ancient race of creatures that somehow evolved so that they obtained the perfect defence. They are quantum locked. This means that when anything living looks at them, they become stone statues. However, when you look away they become living again and can attack you. Lukily with this power they have one major weakness. They can never look at each other or they will be stone forever. They can never be looked at by their own kind. That's how they got the name "The Lonley Assassins".
Now normaly a Weeping Angel looks like...well....an angle that is weeping. However a degenerated or aged weeping angel can look like a regular statue that looks like it was carved by a 7 year old.....or me (it's hard to tell). They are described as the nicest psychopaths in the universe because they let you live to death by sending you into the past and then living off the potential energy of your life had you never left. Another interesting little tid-bit is that the image of a weeping angel (photo and video) can turn into a weeping angel after a while. So while you have been watching them on your screens at home....have they been watching you?
Stephan Moffat must have been on brilliant pills when he made these creatures. You will find with this guy that he will often take childhood fears (moving statues, the dark, etc.) and give you an explanation, even though he can scare the heck out of you as he does it.
Here are some Quotes from the episodes containing this magnificent race:
"The Angels have the phone box"
"Tracked you down with this. This is my Timy-wimey detector. It goes ding when there's stuff. Also it can hard boil an egg at 30 paces, whether you want it to or not, actually, so I've learned to stay away from hens. It's not pretty when they blow."
The Doctor (after finding himself beat and trapped): "Did I mention we have comfey chairs?"
Angel Bob: "We have no need for comfey chairs"
The Doctor: [amused] "I made him say comfey chairs!!!"