「Conspicuously flashing (sharp) pearly whites with opened tonguing mouth of sitting service provider (匕 so popular in dynastic China)」refers to a fellatrix and the source of an event which seems about to occur directly before her face, or, is then occurring in her face…of course, this may refer to the performance of agreed-upon services, but also to the threat of biting off the head of the live snake as might a circus geek. Clearly, becoming the recipient of actual fellating or cunningling [sic] is preferably a lifelong pleasure, not to be enjoyed「just once.」…but someone baring teeth and explaining what may occur 'or else' is not soon forgotten, and need be stated ONLY ONCE to the wise. Naturally, the action of the head being bitten off of a snake-like appendage will likely occur ONLY ONCE to that particular appendage, unless reattached somehow, made ever more unlikely if chewed.
When used as an element, merges「opened tonguing mouth」with「loose and dripping」(厶) as in 郎, and as in either what may occur if the threat is taken lightly by the client, or, if the contract is consummated with a successful conclusion…also likely to occur JUST ONCE in both cases, since the latter requires a period of refraction before regaining virility, and the shaman will likely want to turn her tricks without delay. Needless to point out is the fact that after mastication of the client's meat, such an event will occur ONLY ONE TIME. Included in the element meaning「to eat」(食) by adding「person」and「biting」that indicate someone sitting down to eat meat.
Formerly perhaps「tonguing sitting person, sex-slave, slashed appendage spewing venom」(皂) as JUST ONE, ONLY ONE, JUST ONE TIME that indicates the appendage is infected with a serious illness and/or will be been bitten off and completely severed,「bitten off meat in tonguing mouth, chewed unmercifully.」…not an uncommon practice among very unhappy escorts and one that encouraged the increased use of no-longer-integrated feet initially for penile insertion rather than mouths containing teeth. Such an event could possibly happen only ONCE, ONE TIME in one's life back in the good ol' days prior to emergency surgical reattachment procedures (if not chewed into bits first).

External source definitions …excluding politically incorrect concepts and other meanings deemed offensive today; may include extended definitions, euphemisms, and mnemonics)
Chinese: one grain
Japanese EDRDG: fragrant, grain
Unihan extended: kernel, seed; enjoy, feast [?]