The Swiss believe it is cruel for certain sociable pets to not have a companion. In order to keep guinea pigs, rabbits, parakeets and other pets deemed “social animals” content, you must have more than one.
There are even companies that will rent you a guinea pig to be your pet’s companion should one pass away, giving you time to find a worthy replacement friend.
For cats kept indoors, you may have just one, but you must provide a window where they can see another cat or give it some outdoor time.