「Copulating within orifice」of one kind or another or「counter for animals with rod in reciprocating motions」describes the manner in which most mammalian animals copulate most of the time. Clearly however, there are exceptions to this general rule, particularly with regard to human beings: in any case, a client in dynastic China copulating with a set of no-longer-integrated feet rather than「copulating within some sort of an orifice」would leave less than four feet/legs available among the pair for other functions, such as standing, walking, fleeing, dancing, and so on.「Copulation within enclosure」of some sort, such as a pen or fenced area, again is suggestive of herd asset animals kept for their meat.
　Many cultures, including China, equate snakes as the epitome of a penis and for some obvious reasons, but there are other less obvious reasons known to herpetologists. When it comes to「copulating within orifice」the male snake takes the cake:
　「A hemipenis (plural hemipenes) is one of a pair of intromittent organs of male squamates (snakes, lizards and worm lizards). Hemipenes are usually held inverted, within the body, and are everted for reproduction via erectile tissue, much like that in the human penis. Only one is used at a time, and evidence indicates males alternate use between copulations as a behavioral means of increasing sperm transfer when the interval between copulations is relatively brief. The hemipenis itself has a variety of shapes, depending on species. Often, the hemipenis bears spines or hooks, in order to anchor the male within the female. Some species even have forked hemipenes (each hemipenis has two tips」[for a total of FOUR…see 虫 as its original meaning of snake, snake-like].
　　[　https://en.wikipedia.org/wiki/Hemipenis 2014-06-23　]　
　It may be purely coincidental, but both 'four' and 'death' share the same Japanese pronunciation. The number four is superstitiously associated in the Orient with death, the fate that awaits those who「copulate within an orifice.」…prevention of transmission of sexual diseases was one reason the Chinese invented foot dis-integrating of little girl service providers for masturbation use by adult males.
　Nevertheless, FOUR also represents the count of potential sites available for short-term rental by clients, perhaps concurrently, in the two no-longer-integrated feet and groin region of a female service provider of dynastic China treated as an animal: see 㗊, 田 as four「copulation orifices.」
　「Two twos, turgid flaccid and do it again turgid flaccid」(亖) equal four. Replacement glyph for 肆 (「long time loose and dripping, then do it again」) see that glyph for details.「Copulating within orifice(s), enclosure」suggesting FOUR legs (if humans, and if assuming the minimum number of participants regardless of the sex of each, and if not a selfie situation).
　Suggestive of one orifice or the other of a ewe, a popular four-legged animal for engaging in praiseworthy zooerastic pleasures…or so it has been touted. Perhaps describes one participant being down on all FOURS in the lordosis position with the buttocks spread and available orifice(s) readily accessible, a commonly employed technique of the female of many species to pique sexual interest in surrounding males (such as cats, rats, horses, apes, and so on) by revealing the「copulation orifice(s)」while mooning. Anciently, the Chinese did not use missionary positioning, which is a less satisfying position all around. The missionaries came with the missionary position only a few centuries ago, not the Asians…the religious right came much later and with less frequency, or they did not come…not at all.
　The numerals one through ten are all associated with hand gestures, used in China to avoid confusion while bargaining or simply due to pronunciation problems using different dialects, or while bidding at an auction and keeping the bid quiet. The thumb was tucked under the four fingers and held in the palm and not seen when gesturing FOUR. Note the similarity with「counter for animals」(匹) with「rod」that appears as if the enclosure has been opened and four-legged animals are passing through the open area while being counted, suggesting FOUR-legged domesticated animals.
　Needless to point out perhaps is that this glyph commonly used today to mean「four」is comprised of「copulation within orifice」and 田 meaning「slurry muck pit, wet soil paddy, filled plugging orifice(s)」contains four orifices that are adjacent but not at all resembling the shape of original rice paddies.

Modern definitions (that generally disregard history) …excluding politically incorrect concepts and other meanings deemed offensive today; may list only pigeonholed definitions, euphemisms, or meaningless mnemonics)
Chinese: four; 4
Japanese: four
Unihan extended: four
EDRDG: four

Used within names (nanori)
あ　･　つ　･　よつ