She tested the thought processes of 15 of them by attaching fish and biscuit treats to one end of a piece of string, placing them under a plastic screen to make them unreachable and then seeing if the cats could work out that pulling on the other end of the string would pull the treat closer.

...unlike dogs (which Osthaus has previously tested) no cat consistently chose correctly between two parallel strings. With two crossed strings, one cat always made the wrong choice and others succeeded no more than might be expected by chance.

Okay, she missed two key points here. One, she put a string under a thing. That makes it mind-blowingly interesting, no matter what might be attached to the other end. And two, like other people have said, cats are picky about their treats, and I'll bet money that the cats in this test weren't hungry.

"If we know their limits we won't expect too much of them, which in turn is important for their welfare. I am not trying to say cats are stupid, just they are different. We are so anthropomorphic we can't see the world through their eyes."

No, you've anthropomorphized them so much that you expect a cat to behave like a person. Bad scientist. Bad. No biscuit.