River barely blinks at them LOL! He is so used to me training other dogs, bringing new dogs home for long or short term. Service dogs in training, foster dogs, pet sitting...
He isn't very playful anymore and he kind of ignores other dogs a lot of the time but he is very tolerant and respects dogs he doesn't know well. He can be very cautious with food etc. For example when I had Gomer I gave him (Gomer) a treat but he was to insecure to eat it so he just lay there with the treat in front of him. So River seeing that it wasn't getting eaten really wanted it but he doesn't want to challenge another dog. So he will very slowly and carefully step into their space and inch forward a bit at a time, testing to make sure the other dog is okay with it. Almost like if I was shaping him to pick up an item, each time waiting to see if he is going to get a click, but in this scenario he is waiting to see if the other dog is going to react or protest in anyway. Then wants he decides it is safe he will snatch it up.
It is actually kind of funny because he is a very food motivated dog but he is also a submissive dog too.