I have had Rocco my 10 month old cat for about 2 months. He's very friendly and outgoing. I just recently adopted rusty about 5 days ago. He's an older male about 3 years old. What is normal behavior to expect? I have seen the younger one hiss and growl many times. I have also noticed the bigger cat will follow the younger cat and then run at him. Every now and then the bigger cat will trip the younger cat then jump on him and they go at it for just a second. How long should this go on and is it normal? Thank you