Just like they programed the winter soldier into Bucky, the programed "the hound", a headspace modeled after a hunting dog. An accident leaves Bucky stuck as the Hound and Tony trying to care for a distrustful and snappish "dog" while he waits for Steve to come.

Leashes and muzzles are okay, but I'd like to see some trust built up between them despite their mutual fear/distaste in the beginning. Also Tony gaining some insight into how Hydra treated Bucky (and perhaps relating to some of it).