¿Quién es ese otro perro?

Had a trip to the garden centre for another sack of puppy kibbles - he's growing really fast, but in length rather than girth. All gangly legs which he trips over sometimes. Luckily the rogue macaw was nowhere to be seen, although he did suddenly appear just as we were going. He was eyeballing the puppy with intent, but said canine didn't notice so didn't freak out. What did disturb the young chap however was catching sight of a weird dog in a mirror. Also metal trollies being moved: the wheels drive him crazy and he snaps at them.