「Buttocks, ass chewing」possibly as the ABSOLUTE LIMIT, the natural RESTRICTION BOUNDARY of what a human being will not do, otherwise known as anilingus. Or, reaching the absolute limit of what a person can tolerate until exploding in anger, source of the English expression「giving someone an ass chewing」not unlike a mad dog might. Or on the contrary, perhaps「ass-chewing」as being angry with someone to the absolute tolerable limit and bawling out the person, the limit to any situation of poor quality as exemplified by someone gnawing off the penis all the way down to the ass hole…if so, reaching the absolute LIMIT is slightly more allegorical for「human buttocks」「gnawed, chewed」in the FINAL PERFORMANCE OF THE DAY, and as a COUNTER FOR SLICES AND CUTS: right elements of「tonguing mouth fellatrix」but here as「using teeth directly on meat.」Someone chewing the front meat would ULTIMATELY reach the ABSOLUTE LIMIT, the natural RESTRICTION BOUNDARY, after EXTENDING AS MUCH AS POSSIBLE only after reaching the buttocks from the inside…those sages did have a sense of humor it seems, but sometimes a somewhat warped sense of what was humor at times (blame the wine).
Border, LIMIT, and boundaries relate to a line between different jurisdictions or administrative districts, zones, village sections, town quarters, all areas with a separate set of laws, rules, and regulations.「Sloped soil walls with tonguing service providers」describe these borders, normally patrolled to limit unrestricted access across the lines with gateways and low walls if within a city, checkpoints, document verification and medical inspection stations enforcing quarantines if necessary. Borders encompass areas ranging in size from a country down to a small neighborhood.
「Slope gnawed, chewed up」as the absolute LIMIT may refer to the entire slope from top to bottom utilized for terrace farming and growing crops, a COUNTER FOR SLICES. Use of terraced slope farming methods that were EXTENDED AS MUCH AS POSSIBLE up and down each slope to reach the natural RESTRICTIONS at the top and bottom of the hill's slope, the FURTHEST EXTENT, the absolute BOUNDARY and being able to progress no further, EXTENDING AS MUCH AS IS HUMANLY POSSIBLE until encountering a natural BOUNDARY.
Note that the actual「gnawing of buttocks」and in particular the anus, is not recommended as a best practice…see「parasitic pinworm infestation」(蟯) that can also infect other mucous membranes, worms that also「gnaw yer ass」to the absolute limit, and an Escherichia coli infection in one's upper gastrointestinal tract may kill by causing severe anemia or kidney failure.

External source definitions …excluding politically incorrect concepts and other meanings deemed offensive today; may include extended definitions, euphemisms, and mnemonics)
Chinese: limit; bound; to set a limit (on)
Japanese EDRDG: limit, restrict, to best of ability
Unihan extended: boundary, limit, line