The law of conservation of cats, also known as the principle of cat/feline conservation, states that the number of cats in an isolated system (closed to all further adoption or other forms of acquisition of new cats) will remain constant over time. This principle is equivalent to the conservation of energy, in the sense when energy or cats are enclosed in a system and none is/are allowed in or out, its/their quantity cannot otherwise change (hence, its quantity is “conserved”). The number of cats in an isolated system cannot be changed as a result of processes acting inside the system. The law implies that the number of cats in an isolated system cannot be altered, although it may be rearranged in space and changed into different cats; such that every time a cat “owner” lets one gray cat out of the house, a second gray cat will come back into the house, and for every red cat that exits the house, another red cat will enter, and especially if a red cat and a gray cat both leave the house at the same time, another red cat and gray cat will stumble all over each other rushing back into the house before the door can close, no matter if it is four in the afternoon or three in the morning, even if they have been let out and in fifteen times in the past hour, because the number and color of cats going out of the house must be equal to those coming back in.
This seems tangentially related: http://garfield.nfshost.com/1986/02/09/
have ye n’er heard of cat ladies ‘n cat horders?