Why does my cat become suddenly jumpy?

My cat is about 3 years old and lately all of a sudden she gets very frightened, and starts looking down at the blanket and other things sniffing and relunctintly pawning at the object almost like she trying to figure out if its alive or a threat, and if you move the item shes staring at, she jumps back quick. She gets in these modes about 5-6 times a day but not sure what triggers it. Its an uneccessary stress for her. Shes a very loving cat and is not frightened of people. This is my theory my girlfriend thinks im crazy but i purpose that its an instinctual reaction to snakes. Cats get there hiss from snakes because to them they are a dangerous animal. so they have evolved to be wary of long moving objects. Also cats and snakes lived side by side and hunted the same prey for 1000s of years. so even though a cat mayh never seen a snake they know to be careful of them. Thats why kittens love to chase lons. They have to learn what snakes they can eat and what to stay away from.