cute dogs, cats, and other animals

Whats the resource here?

The man is the barrier. The dog knows he isnt supposed to cross the man, and so gets aggressive towards the other dog.

But there doesnt seem to be any toy or treat or anything to guard. And that doesnt explain the loss of aggression upon removal of the barrier.

Barrier frustration is not the same as resource guarding. Think of it more like a reaction to anxiety from not being able to get to or interact with something of interest. Over time that anxiety gets displaced from the barrier to the object itself, and can also build up into an extreme short-circuited reaction.

But when the barrier is removed often the anxiety goes away and everything is fine.