Belle is a spayed tortie, just shy of 3 yrs old, front declawed. She hisses @ strangers, but otherwise is well-behaved--until the last couple of months. She saw a neighbor's cat outside and went bonkers (hiss, growl, fluff...), then attacked my boss' leg. She's attacked periodically since. Today (unprovoked) she did the same, but added a nasty bite. A few months ago, she dispatched a couple of mice, but normally she doesn't encounter "outdoor" animals. She's an indoor-only and is the only pet. Any ideas why the sudden change in demeanor?