Cats and dogs don't understand string theory.

Except for my cat, who's a beautiful genius. From New Scientist:

Now we know why cats never get bored of chasing string. A new study has found that domestic felines don't seem to understand cause and effect connections between objects.

Chimpanzees, tamarin monkeys, parrots and ravens all understand that tugging on one end of a string will bring a treat at the other end closer. Pigeons and human infants don't; and cat lovers dismayed at their pets' lack of nous can console themselves with the knowledge that dogs don't either.

"There's no reason to think that cats are more stupid than dogs," says Britta Osthaus, a comparative psychologist at Canterbury Christ Church University, UK, who led the study. "I've done quite a few tests and I always find that dogs just don't get it."

Working with 15 shelter cats, Osthaus's team attached fish or biscuit treats to one end of a string. A plastic screen with a small gap at the bottom separated cats from their reward, requiring the felines to tug on the string to get the treat.

With a single string attached to the food, most cats learned to paw at the string to get a snack. But when Osthaus' team introduced a second piece of string, unconnected to any foods, cats tugged on the correct string less than half the time.

This suggests that the cats couldn't infer cause-and-effect relationships between two objects and could only learn an association from scratch each time.