Without his being really aware of it, the sight of the rubbish bags had warned Peter to be alert for several things, including a rubbish truck stopped or slowed around the corner, and dogs and rubbish collectors running over the road. The dogs are likely to be there because:
(a) They like to scavenge in rubbish.
(b) They like to chase rubbish collectors.
(c) The weekly meeting of the local canine obedience society is held on rubbish days.