「Illness of sheep」may instead refer to scrapie, a degenerative prion disease that causes sheep and goats to SCRATCH themselves against objects continuously or chew their own hide as the animal's central nervous system and brain deteriorates into mush. With anatomy lacking fingernails, hands and fingers to scratch itself, a sick sheep also uses its mouth and teeth to chew aggressively on its own hide as a means of scratching an itch as it loses its mind:「illness of sheep chewing with emphasis.」
　No doubt the sages also intended this combination to depict a particular fondness for sheep above other forms of sexual intercourse, with ITCH being the feeling of wanting to spend some quality time tupping one's favorite ewe in a「praiseworthy and recommendable, beautiful experience」and「remaining traces of the past with a good sheep.」Furthermore, getting too close and making physical contact with sheep causes SCABIES mites to seek a new host…the warm, moist area of a human crotch is a perfect habitat. Perhaps depicting an「illness」that is caused by「sheep」and may be referring to the fact that wool (yarn spun from hair fibers shorn from sheep) is a bit ITCHY at times. Yet, a mere ITCH hardly constitutes an「illness.」
　「Physical condition with sheep-like and really good emissions spurting」as the appearance of copious vaginal froth on the surrounding fringes of the vagina, labia, and (if any) the penis, that slithers continuing to the anal orifice, causing a TICKLING SENSATION: during ovulation of a female human and estrus of other animals such as sheep, the individual can become more sexually aroused than at any other time. Adding a dildo and/or an actual penis with enthusiastic action acts just like a kitchen whisk with frothy white discharges whipped up and resembling egg white meringue, mousse, cotton tufts and tassels, or sheep wool, and when observed causes great excitement. Froth is pumped out spurting from the vaginal orifice about once per second as the muscles contract and release during successive waves of orgasm, forming what appears to be virgin sheep wool surrounding the quivering orifice.
　「As a woman's cycle progresses, the mucus secreted from the cervix will change due to hormonal fluctuations. A woman is considered to be ovulating and fertile when the mucus is clear, stretchy and slippery, and looks like egg whites.」
　　[　https://ic.steadyhealth.com/most-fertile-cervical-mucus 2017-05-03　]　
　「Understandably this 'foaming at the mouth' phenomenon has your nerves on edge. But, if you were recently tested for sexually transmitted infections (STIs) and received a clean bill-of-health, most likely the foam-like substance is just a result of the combination of two art forms: The Joy of Sex and The Joy of Cooking. The main ingredient here would be semen…. Semen is loaded with protein, a pinch of sugar, and a dash of salt. The dildo and your boyfriend's enthusiastic 'mixing' inside of you acted just like a kitchen whisk.」
　　[　https://goaskalice.columbia.edu/answered-questions/foaming-after-sex/ 2017-05-03　]　

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: to itch; to tickle
Unihan extended: itch
EDRDG: itchy