I work with animals, mainly dogs and cats, and I have to say I'm more afraid of cats than I am of dogs (even though I love 'em). Cats have a Jekyll and Hyde personality and the smallest of things can touch them off like a stick of dynamite. One minute: sweetness & hearts & flowers. The next minute: thunder & lightning & fireballs.
There's a cat that I take care of quite frequently called Sweden. He's a rescue off the street and lives with a cat called Bella. Sweden is all over me when I come in - rubbing himself around my leg, purring like crazy and then wanting 10 minute belly rubs after he's eaten. But inevitably, the "switch" will flip. Usually the trigger is when I'm scooping out the litter tray in the back room, or when Bella (who's the clumsiest cat I've ever met) lands awkwardly from a height when she's playing. All of a sudden his ears go back, he gets this look in his eye and he just starts walking towards you like he's stalking prey. That's my cue to get the hell out of the apartment because otherwise he will literally tear my legs to shreds. One time he went for me as I was scooping the litter and I had to back into the bathroom and shut the door on his slashing claws. He sat outside the bathroom door and did that low kitty moan constantly for about 20 minutes. I was trapped. Every time I opened the door even slightly, the claws would come through and he'd go into a full scale war cry. I had no phone on me, no way of getting out. Eventually I had to be a bit nasty and push him away with a broom (which I was afraid to do because it might make him go outright thermonuclear).
One time he chased me out of the front door and I was carrying a bag of trash. I had to close the door so quickly to escape his claws that I inadvertently closed the door on the trash. The next few seconds were characterized by an explosion of ripping, tearing and howling, and what I ended up with was basically the top of the trash bag with nothing else in it. I had that little mess to clear up on the next visit.
I managed to capture his death stare one time when he "escorted" me out of the apartment. This cat seriously gives me the chills. But before the switch flips, he is such a cutie pie.