That sounds like some weird old timey lesbian thing. However, more importantlySaint Magdalena de Pazzi is said to have cured a nun of sores and scabs in 1589 by licking her limbs.
The kid did say it was an old belief and all but it's definitely not something we should still be doing. Dude lost a thumb from his own germs.There are potential health hazards in wound licking due to infection risk, especially in immunocompromised patients. Human saliva contains a wide variety of bacteria that are harmless in the mouth, but that may cause significant infection if introduced into a wound. A notable case was a diabetic man who licked his bleeding thumb following a minor bicycle accident, and subsequently had to have the thumb amputated after it became infected with Eikenella corrodens from his saliva.
The human mouth is full of germs and the saliva is a good vector for infections.