They're like buses, but they come around even more regularly...
This is the horrifying moment a man who had bravely intervened to stop a 'berserk' dog from attacking commuters in South London is mauled by the savage animal as it turns on him.
Video filmed by locals in flats overlooking New Malden railway station in Kingston-upon-Thames shows the moment the 'irresponsible' dog owner lets go of one of her leads as it tears free from her grasp.
She doesn't let go, the beast pulls it from her hands in its eagerness to maul the man. He's very very lucky he wasn't more seriously injured.
Officers seized the dog following the attack, and its 22-year-old owner was arrested on suspicion of being in charge of a dog dangerously out of control. She was released and remains under investigation.
Armed police should have dealt with it then and there.
A witness told The Evening Standard: 'I had another neighbour say that these same dogs have attacked a little dog in Beverley Park in the past so this didn't seem the first incident.'It never is, is it?
'Their owner should have them muzzled if that was true. The owner was irresponsible, it doesn't look like the dogs have any training at all.'
Au contraire, it looks like they have been trained exactly for this sort of thing...