Kissing

A kiss is the touching of one person's lips to another place, which is used as an expression of affection or to show respect, and as a greeting or a farewell; kissing can be used to express romantic affection or sexual desire. The word comes from Old English cyssan "to kiss", in turn from coss "a kiss". It is generally considered one of the strongest ways to show affection.

Kissing is a complex behavior that requires significant muscular coordination; in fact, a total of thirty-four to thirty-six muscles working cooperatively. The most important muscle involved is the orbicularis oris muscle, which is used to pucker the lips and informally known as the kissing muscle. The tongue can also be an extremely important part of the kiss. Lips have many nerve endings so they are sensitive to touch and bite.