Okay so this might be long but it’s really messed up!

We moved into our house 3 years ago. We have a HUGE back yard and at the end of it in the left corner we have neighbours. There fence was falling apart but they didn’t seem to care, we have a huge dog. Akita and German Shepard about they have a medium sized dog... now, dogs will be dogs and obviously they are going to bark at eachother here and there! That’s fine, I let them do there thing for a while! My dog NEVER barks. He will stand up at the fence and watch the little dog through the Lattice while this dog goes fucking ballistic. It barks at everything, even if I go to take my recycling out 60 feet away from their backyard... he will bark! (Side note: we put up at 6 foot fence not long ago where there shitty fence is but on our side just because my dogs tall and there fence was only 5 feet tall and the husband of this evil women did thank me) Everything was okay for a year then I noticed my dog started to get aggressive. Not anything bad but his tail would go down, hairs stand up and he would just stand near the fence facing it. Not doing anything, not moving, not barking but just standing their... I can tell my dog wasn’t playing and something was up. The thing is the neighbours dog wouldn’t even be outside when he did this... the neighbour women was. Odd right? So I started hiding in our garage doorway where she couldn’t see me and that’s when it started. She would walk over and stair at him... telling him to fucking die, useless piece of shit, he needs to be killed, piece of shit animal, would call him over to the fence and antagonize him and try to get him going then say awful shit, slam her hands on the fence... after she called him over! She’s doing and saying ruthless stuff... LIKE WHAT the actual fuck. My dog does nothing wrong, he’s curious I’ll give them that but I always go and get him... but since our backyards like so fucking big it takes me a minute to get there. Now, the other day near there fence I found FIVE already dead mice, they weren’t killed by an animal and they looked fine but we’re dead. I seriously thought forsure she poisoned these mice and tossed them over to my dog for him to eat and he did, he was puking after and just not himself. He didn’t get much of the one mouse because I chased him down and made him drop it but still... that’s just really weird. Am I insane to think he potentially poisoned these mice and threw them over the fence? I think its odd five mice that looked fine were dead right around where there fence and yard is and the face she is so aggressive about my dog doesn’t help. Idk it’s just insane to me... even though their dogs annoying AF I wouldn’t wish death. Dogs will be dogs, they bark!