The question contains one of the reasons why domestic cats sometimes like to snooze or sleep inside a bathroom sink. I am referring to the phrase “chill out”. The bathroom sink is uniquely placed to provide certain benefits to a domestic cat particularly while living in a hot environment. Due to global warming, and thinking of the southern states of America, there may be some hot homes if they are without air-conditioning.
The bathroom sink is likely to be cooler than surrounding areas such as carpet or upholstery on furniture. That cooling process would be very welcome to an already slightly overheated domestic cat. Imagine wearing a coat permanently when living indoors or around the home in a hot climate. It must get a little bit irritating for the domestic cat. And therefore snoozing in a sink makes sense. A bathroom sink is probably cooler because it is a large, solid mass which maintains its temperature and it is cool down by its use in often containing cold water. I would welcome input on that topic by a visitor, by the way.
Vertical travel, raised space
There are other advantages. One is obvious which is that the sink is raised off the ground. Domestic cats like to move vertically as well as horizontally. We all know by now that domestic cats need vertical spaces in order to rest and exercise themselves. It provides reassurance and a chance to express natural behaviour.
Protection is associated with vertical spaces. The sink, however, provides a domestic cat with protection all around them but not above them. I’m sure that cats would like a ceiling above them as well but they accept what they can get which is protection from all sides. This is welcome and also a reassurance to them.
Reassurance through pressure
There is another subtle benefit for a cat. I’m going to equate a cat’s liking of sinks to their liking of cardboard boxes. It is universally accepted that cats like to rest inside boxes. Sometimes the cat is much too big for the box but they still manage to squeeze inside. The theory is that when a newborn and growing kitten is being nursed by their mother they have the reassurance of being surrounded by their siblings who press against them.
The youngsters carry forward this feeling of reassurance through the pressure of a surrounding cardboard box or a ceramic sink. I’m referring to the pressure on their bodies. It is an interesting concept (that I started I believe!) because a well-known calming cat and dog harness, called the Thundershirt, works on the basis of applying pressure to the flanks of a cat or dog. It is a successful product, so successful that when domestic cats wear it they tend to flop over onto their sides until they get used to it. It has a similar effect to a mother picking up a young sibling in their jaws and carrying them to a new den. I call it the “kitten effect” because the mothers jaws applying pressure to the back of the neck makes the kitten become passive assisting the mother in transporting her offspring to the new den.
Domestic cats often seek reassurance in all kinds of ways. For example, they sniff their human companion’s bed as a reassurance that the bed has been slept in by their guardian and the want to smell that scent. Bedrooms are central to domestic cat’s home range because of the heavy load of scent on the bed. Scent exchange (rubbing with flanks and cheeks) is also a form of reassurance.