After a quick butt-sniffing "hello" they are literally at each other's throats.
In short order we have a 2-dog Tornado on our hands.

What Rudy lacks in size, he makes up for in raw, untamed ferocity! Here he is in mid-strike. Rudy runs circles around Dozer, them jumps up on the couch, using it as a springboard to launch himself back on top Dozer.

Eventually we can't take it anymore and both dogs end up in jail!!!