When Peter hit the horn, the noise alerted the dog to the bike's presence and it abruptly stopped, then turned tail and moved back to the footpath.
But, as Peter passed, it suddenly decided that here was a neat thing to chase and came out at Peter's bike, barking as it ran.
(a) took a kick at the dog
(b) braked hard so that the surprised dog passed him. Then Peter, on his bike, promptly chased the dog.
(c) countersteered hard to get around the tight corner he was entering, hoping to leave the dog behind.