About 7 weeks ago I bought a 12 week old GSD, about a week later my wife's cat needed to be euthanized so next day we go to the animal shelter and adopt a 4 year old Maine Coon Cat, fairly large cat. The curious pup wanted to figure out what it was but when the pup got close the cat would hiss and run away.
This went on for about 4 weeks, finally the cat stopped running, the pup would get close and the cat would swat at him (claws in) pup started backing off. For a while when the two of them would pass in our narrow foyer the cat would stop and the pup would slowly approach as soon as he got to the cat he took off like a shot.
I guess boundaries were set, now the pup goes up to the cat and if the cat swats at him with his paw the pup would just swat back with his paw, it's funny the almost look like they are playing