 In 2009, an experiment was conducted where cats could pull on a string to retrieve a treat under a plastic screen.When presented with one string, cats had no trouble getting the treats, but when presented with multiple strings, some of which were not connected to treats, the cats were unable to consistently choose the correct strings, leading to the conclusion that cats do not understand cause and effect in the same way that humans do.Cats have complex dreams while sleeping, retaining and recalling long sequences of events while they are asleep, as many other animals do.