oldunova/Getty Images Harrison believes cats who favor lying on their sides are relaxed ... koldunova/Getty Images Spotting a cat sleeping on its back, showing its belly, can often look hilarious ...

A cat laying on decking by a fireplace outdoors ... Teller said, when a cat is on its back, with its belly up, these are signs that the animal "trusts you and is willing to expose vulnerable ...

Cat owners have no doubt seen this before: While lying down—on the back of the sofa or on your lap—your kitty is swishing its tail. Like most cat behaviors, this one is tough to decode.