「Intercourse and leaving a trail of sticky fluids」suggests not yet understanding the RIDDLE, ENIGMA, PUZZLE, CONUNDRUM of infectious disease and the mechanism by which they spread.
　「Words that are perplexing, confused」or「intercourse motion with puckered anus」or「intercourse with feet motions and sticky blobs」to represent as any sort of RIDDLE, PUZZLE, etc. Clearly, at least in female bonobos and human beings, the anal orifice is no longer conjoined with the vagina as it is with birds, reptiles, and other cloacal animals, so one could argue successfully that engaging in「sex actions with a puckered anus」does exhibit a degree of CONFUSION, unless performed deliberately. Perhaps sex ought not to be confusing, so if it is, there must be some other agenda besides just plain intercourse that needs to be solved as a RIDDLE, ENIGMA, PUZZLE, CONUNDRUM.
　Nevertheless,「intercourse with feet motions and sticky blobs」actually at first solved many problems and was why it became so popular in China, PUZZLES and CONUNDRUMS such as: controlling the populace with a religious theme that would attract devotees and adherents and keep them returning enthusiastically for more, stopping runaway slaves and asset loss, obviate biting for revenge while fellating and associated compensatory damage payments, mitigate the spread of disease and infection due to contact with mucous membrane(s), eliminate miscommunication of directives to ewes, maximizing profits under centralized management and control, establishment of feeder enterprises in a vertically-structured conglomerate supply chain fulfilling a full array of economic demand, establishing professional level skills to limit competition via monopolies and secure client dependence, and so on. In short, how to become a gazillionaire by selling sex slavery services.
　From a modern perspective the RIDDLE becomes: why did「intercourse with feet splats」have so many「enthusiastic fanatics」?

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: riddle; see 謎兒|谜儿, riddle
Japanese: riddle, puzzle, enigma, mystery, enigmatic, mysterious, a particular type of riddle, to be enigmatic or puzzling, to be wrapped in mystery
Unihan extended: riddle, conundrum; puzzle
EDRDG: riddle; puzzle; enigma; hint; tip