Saber-cats. I'm playing a new character, Bosmer archer/thief. I'm super sneaky, as I am a barefooted elf skulking happily through the woods.
Turns out the cats are pretty sneaky, too. And they more often than not, just look like shaggy lumps of tundra while they're laying about, getting their 13-20 hours of sleep per day as cats normally do. So I often stumble across them at uncomfortably close range.
Bears make a racket, it's easy to know when one's around. Cats sleep until you put your foot down on them, then it's a blender of claws and teeth.