Vulnera Sanentur is a healing spell created by professor Severus Snape, able to heal injuries ranging from minor cuts to deep gashes. The incantation, which sounds "almost like song" sometimes must be repeated up to three times in a row to have maximum effect.
When the spell is used the first time, the flow of blood eases up; the second time causes the wounds to knit; the third time removes most visible injuries near-instantaneously. It is unknown whether the spell always needs to be cast three times, or simply in the unique situation caused by Dark magic. The victim would still require medical treatment, but if dittany is applied immediately, scarring can be avoided.