It will cause outrage among some cat owners, but research suggests the pets are not as clever as some humans assumed – or at least they think in a way we have yet to fathom.

Psychology lecturer Britta Osthaus says cats do not understand cause-and-effect connections between objects. 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.

They were tested in three ways, using a single baited string, two parallel strings where only one was baited, and two crossed strings where only one was baited.

The single string test proved no problem, but 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.

Osthaus, of Canterbury Christ Church University, Kent, said: "This finding is somehow surprising as cats regularly use their paws and claws to pull things towards them during play and hunting. They performed even worse than dogs, which can at least solve the parallel string task."

The study helped show the limits of feline intelligence, said Osthaus, who conducted the research while a teaching fellow at Exeter University. "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."

There is just one consolation. Humans don't understand string theory either.