Mittens a murderer

Mittens is the feline companion you've loved since kittenhood, curled up beside you at night, soft purrs lulling you to sleep. However, lately, Mittens' behavior has been peculiarly peculiar. You find the cat sitting upright, unblinking, gazing at you with an almost knowing expression. The other day, you heard Mittens meow your name with flawless pronunciation. Even more strange, Mittens seems to understand every word you say, responding to complex requests with a level of intelligence that's far from typical for a house pet. The comforting familiarity has taken on an eerie edge, as if you're sharing your home with... something—else.