The sounds the toy dog is making at the end fill me with sadness.

good dog

Oh man I had a dog like this once.

jesus christ kill it already. it sounds like it's sobbing. put the damn thing out of its misery!

A really bad case o' the asthma.

Toy dog bad.
Whippet good.

All those dreams of catching the rabbit just got replaced by the recurring nightmare of catching this thing.

I imagine a really powerful exchange in dialogue between them, the real dog realizing that not only is her new friend a robot but unaware and now dying---those final moments before the mercy killing are chilling.

I agree with the dog