Kissing Animals

Kissing is a complex behavior that requires significant muscular coordination; a total of 34 facial muscles and 112 postural muscles are used during a kiss. The most important muscle involved is the orbicularis oris muscle, which is used to pucker the lips and informally known as the kissing muscle. In the case of the French kiss, the tongue is also an important part. Lips have many nerve endings so they are sensitive to touch and bite.
Disease transmission
Diseases which may be transmitted through kissing include mononucleosis, allergic reactions to nuts and drugs, and herpes, when the infectious virus is present in saliva. Research indicates that contraction of HIV via kissing is extremely unlikely, although a woman has been infected with HIV by kissing (in 1997). Both the woman and infected man had gum disease, so transmission was through the man's blood, not through saliva.