Ever since I adopted them, my cats normally keep their tails tucked under them so this was rather out of character.
I got a 6 year old female rescue years ago. Two weeks later, my then GF said she needed a friend, so we got a little girl kitten. The hated each other forever. About 7-8 years later they would be taking one of their 75 naps that day and they'd barely be touching. By the end they were good friends not great though.
A little over a year ago, I adopted a female kitten. But she had (and still has) endless supply of energy. I once spent like 1.5 hours playing with her to tire her out and in the end I was the one to tire out. So adopted another female kitten 1 month younger. After the standard introduction, they got along fairly well. But even to this day the older one likes to bully the younger one whenever she's in the mood. After the bullying session (with comical yells for help) end, they'd often sleep right next to each other.
That's such cat-like behavior. My guys do the same thing, hissing at each other one minute and acting completely snuggly with each other the next. I'd kill to be able to know what was going through their little walnut brains.