Apparently this is the「perfect plant, grass」used to weave a floor mat, TULE, BULRUSH. Element details reveal how the plant material mats were used and why using the mats caused SMILES, SMILING, but first remember that floor mats are cushions upon which one sits or lies upon, i.e., a pad under one's buttocks and body rather that a hard, stone cavern floor or some other unpadded surface:「plants, deliberately out of reach, with emphasis on surrounding two copulating.」
「Emerging shafts deliberately surrounding units of money」as service providers working to employ their trade skills with clients, collecting money for their owner the shaman brothel proprietress. Be sure to see the other glyphs with similar meaning and the elements used within them, all leaving no doubt as to the uses of these mats as buttocks padding while seated or lying prone or supine—exactly how mats are still used to this day: as a mattress.
Chinese sources describe an entirely different plant, known in Japan as nanten and that cannot be woven into matting.
Both「inducing an abortion」and an「enema purgative」will generate SMILES when「deliberately」performed at home, with both procedures ridding the body of something unwanted that is expulsed after「two copulating」within a vagina or within an anus, respectively.
Skimmia japonica sports flower clusters followed by bright red berries when a male pollenizer is nearby, a plant that needs consistent flowing fluids to remain healthy.
Scirpus lacustris, also called bulrush and the common club-rush, suggests the rush home after clubbing to just do it.
「Emerging shaft with intimated pedophilic incest」as SMILING or as a COMFORTABLE MATTRESS likely needs no explanation.
「Like humans but unlike chimps and most other animals, bonobos separate sex from reproduction. They seem to treat sex as a pleasurable activity, and they rely on it as a sort of social glue, to make or break all sorts of relationships. 'Ancestral humans behaved like this,' proposes Frans de Waal, an ethologist at the Yerkes Regional Primate Research Center at Emory University. 'Later, when we developed the family system, the use of sex for this sort of purpose became more limited, mainly occurring within families [i.e., incest]. A lot of the things we see, like pedophilia and homosexuality, may be leftovers that some now consider unacceptable in our particular society.' 」
[ https://www.discovermagazine.com/mind/casual-sex-play-common-among-bonobos 2023-05-14 ]

External source definitions …excluding politically incorrect concepts and other meanings deemed offensive today; may include extended definitions, euphemisms, and mnemonics)
Chinese: smile; (district); Skimmia japonica
Japanese EDRDG: smiling, reed used to cover tatami
Unihan extended: smiling; a kind of aquatic herb, clubrush, Scirpus lacustris