Since at least 1973, it has also been used to refer to a sexually attractive young woman. Pornography is often referred to as porn and a pornographic work as a porno. English adopts and uses hentai as a genre of pornography by the commercial sale and marketing of explicit works under this label. A variation on gay twinks this is to place the fingers and thumb on the penis as if playing a flute, and then shuttle them back and forth. Tentacle rape or shokushu goukan is found in some horror or hentai titles, with tentacled creatures having sexual intercourse with female characters. It is also often mixed with other fetishes in practice, such as voyeurism, denial, anime hentai etc. For uncircumcised males, stimulation of the penis in this way comes from the pumping of the foreskin, in which the foreskin is held and slid up and down over the glans, which depending on foreskin length, is completely or partially covered and then uncovered in a rapid motion. The anus has a relatively high concentration of nerve endings and can be an erogenous zone, and the receiver may receive pleasure from external anal stimulation. Along with the penis, the scrotum is sensitive and considered to be an erogenous zone. Some productions mature milfs are noted for sophisticated and/or experimental storytelling and animation techniques. The related term twinkle-toes, which implies that a man is effeminate, tends to be used in a derogatory manner. It may be used as foreplay, or as an alternative to sexual penetration. Shemale is a term primarily used in sex work to describe a trans woman with male genitalia combined with female secondary sex characteristics, usually including augmented female breasts, from breast augmentation and/or use of hormones. Teacher and Student or Boss and Secretary pornography involves sexualized situations which take place between an authority figure, such as a teacher or boss, and an underling, such as a student or secretary, often fake. Each participant may engage in any type of sex acts with one or both of the others, such as vaginal, anal or oral sex or mutual masturbation.