medieval theologian thomas aquinas said of lust:
...wherever there occurs a special kind of deformity whereby the venereal act is
rendered unbecoming, there is a determinate species of lust. this may occur in two
ways: first, through being contrary to right reason, and this is common to all lustful
vices; secondly, because, in addition, it is contrary to the natural order of the venereal
act as becoming to the human race: and this is called "the unnatural vice." this may
happen in several ways. first, by procuring pollution, without any copulation, for the
sake of venereal pleasure: this pertains to the sin of "uncleanness" which some call
"effeminacy." secondly, by copulation with a thing of undue species, and this is called
"bestiality." thirdly, by copulation with an undue sex, male with male, or female with
female, as the apostle states (rm. 1:27): and this is called the "vice of sodomy."
fourthly, by not observing the natural manner of copulation, either as to undue means,
or as to other monstrous and bestial manners of copulation.