A few years ago whilst birdng some local pools i spotted a dog walker throwing a stick for his little Jack Russell. The walker threw it repeatedly near a pair of Mute Swans with 4 young. On the last throwing of the stick the dog disregarded it and instead paddled towards the Cygnets. At this the male Swan fluffed itself up and repeatedly hissed at the animal. Undeterred it carried on after the Cygnets - the adult Swan calmy approached the dog head-on craned its neck over the now apprehensive little mutt reached down grabbing its nape and pushed it below the water whilst swimming slowly backwards.....
Within a minute the poor creature was dead - a salutory lesson to all irresponsible dog-owners.
Chance favours the prepared mind