Slip of tounge.

A classmate  of mine in the marketing  class contributing to the class discussion intending to say "Word of mouth" but ended up saying " Mouth to Mouth" . The entire class bursted into a laughter roare.

Note : Mouth to Mouth is designating a method of resuscitation in which the rescuer breathes directly into the mouth and lungs of a person who has stopped breathing 

To my pervert mind  is a form of kissing  and I assume  my  classmates may be perverts too.