REINS are used to control motion of a head with bindings, a LEASH is placed around the neck of an animal in order to quickly control its movements and to force obedience:「confirmation with penis within tonguing mouth and head sliding」「penile emissions, threads with drag away」seems to describe a rope or other taut binding placed around the neck of a fellatrix (who still possessed teeth within her or his tonguing mouth orifice) for the purpose of assuring that no gnawing or other untoward actions might take place during the procedure, else the fellatrix would be immediately strung up and strangled, likely until expiration…hanged by the neck.
　Or: obviously, a LEASH or REINS could also be attached to the neck of a dog in order to control its tendencies to engage in copulation in the first place, or to attempt an extrication of a dog's bulbus glandis from within a bitch's vagina after ejaculation (not recommended, actually). Male canids, the 'dogs,' are endowed with a very special penis, unlike any other species. A dog is equipped with two glands located at the base of the shaft that engorge and harden upon erection, normally after baculum penetration into the bitch's vaginal orifice (a baculum is a bone located within the dog's penis that enables rapid insertion, i.e., spearing). These locking bulbus glandis swell large enough to prevent the penis from being extracted from the bitch's vagina for quite some time, normally ten to fifteen minutes (or up to an hour in some cases), to allow the dog's semen sufficient time to get enough of a head start toward the bitch's ova that the male might actually sire some pups, completing his mission in life, rather than the next dog waiting to mount the same bitch in heat.

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: leash; rein
Unihan extended: rope, cable; reins; to tie up, bind
EDRDG: tie