Cats have highly developed hearing and can rotate and swivel their ears to zero in on any sound which interests them. Your cat may appear to be sleeping, but look closely and you may notice that his ears will suddenly twist to locate an unexpected sound or in response to your speech.
You can also tell a great deal about the mood of your cat by looking at their ears. If his ears are upright and pointing forward, he is alert but relaxed. If his ears point sideways, he is slightly less comfortable and is listening out for any sign of danger. If his ears are upright but pointing back, he may be preparing for trouble.
A cat in a defensive pose will flatten down his ears in order to protect them, while an aggressive cat will twist his ears forwards. His ears may still be flattened, but the tips will face in the direction of his prey. He does this in order to obtain as much auditory information as possible so that he may launch a successful attack.