In the Doctor Who episode “Blink”, why do the angel statues appear in weird places?

Question

There are two specific scenes I'm thinking of where angel statues inexplicably appear in strange places.

The first is when Sally Sparrow is in the police depot and looks out the window and sees angel statues on the church across the street. When she looks again, they are gone.

The second scene is when the officer is in the basement with all the cars. Sally leaves, and when he turns around, the room is full of angel statues.

You can view the two scenes here;

http://www.youtube.com/watch?v=TJ-ZvimgZ0o

http://www.youtube.com/watch?v=TaAV2PnxGWo

Can anybody explain these two scenes within the rules imposed by the episode?

Answer 1

The angels had followed Sparrow to the police station, and they generally hide themselves in positions where you'd expect to see statues (like the church across the street). But when Sparrow turned her back they went across the road into the police station. Once they got to the carpark there was no need to hide any more so they showed themselves more openly.

Why do they seem to move so slowly in the house compared to out in public? I think the main reason is because it made for suspenseful TV. If you like though, imagine something like "the angels move faster when there are more people not looking at them."