Strictly speaking, licit sex means sex within the license of a heterosexual marriage, both civil and religious, for the purpose of reproduction only. Everything else is illicit sex. That does not mean, as sometimes neophytes infer, that one cannot enjoy the peripheral sexual activities during such time of reproduction. No need to act like a robot on a time plan. Better show affection and be gentle.  

Such sex is godly and divine as Sri Krishna expresses in the BGAII 7.11, version 2:

“I am the strength of the strong, devoid of passion and desire. I am sex life which is not contrary to religious principles, O lord of the Bharatas [Arjuna].”

OT 7.11 is missing! So no version 3 for now.

Other forms of sex are consequently demoniac and are to be abstained from by those humans who plan to elevate themselves in the cycle of birth and death.

Animals naturally follow their instincts. And I suppose there is an animal body available for even the weirdest sexual expressions, which I shall not enumerate.

Everything can be used in Lord Krishna’s service, including the genitals and such engagement is clearly regulated.

While hitchhiking I once met a relatively close Brisbane so-called karmi neighbour. He told me that he had many children. I asked him why he had so many children. He replied that in his (Christian) religion sex is restricted to reproduction only and because he didn’t want to renounce sex altogether, he and his wife simply kept producing children. Way to go, Madam and Sir! On Lord Krishna’s behalf: Thank you very much for following religious principles regarding sex!