Harness Walking causing aggression?

[Jaclyn33]

Hi Everyone,
I have a pair of bonded 4 year old domestic short hair cats that I started harness walking about two months ago. They absolutely love it, they'd live outside if they could (well maybe, we're not letting them find out if they'd really like to live outside).
As much as they love it, I started noticing a bit of aggression between the cats shortly after I started them outside. It's nothing serious, a hiss or a smack here and there, and most of the time they still get along perfectly. They often sleep side by side, so I'm not overly concerned, I'm just wondering if this is something that anyone else has noticed at all.
I expected that taking them out would help them release excess energy and I would not have expected aggression to stem from that. Thoughts?

Side note: 2 weeks ago we did adopt a rescue puppy, so that has definitely stirred the pot even more, but what I'm talking about predates that by several weeks.

 

[Mamanyt1953]

My best guess, although I have NOT experienced it, is something along these lines:

Cat One: Did you see that robin?

Cat Two: That was a FINCH, you idiot!

Cat One: ~SWAT~

 

[susanm9006]

Some cats get over stimulated by being outdoors. Others get crabby because they don’t like being brought in from outdoors. And still others pick up scents that makes previously friendly cats unable to recognize one another. Could be any of these reasons. If you have just started taking them out this may pass or you may find that it worsens. I think you need to watch the behavior and if the stress seems to be increasing you may want to cut back or eliminate the outside time altogether.