 Cats can be confusing creatures. One minute they are snuggled up on your lap, and the next they are giving you the cold shoulder. You might even feel a little offended by your cat's mood swings, or at the very least, perplexed. Perhaps an older cat is jealous of the attention being lavished on a new kitten, if a docile cat suddenly becomes aggressive, taken to a veterinarian. Some medical conditions, e.g., hypothyroidism, can make a cat irritable, leading to cranky behavior. Cats can also contemporarily help a cat relax.