Sur practice involves the offering of smoke (burnt food substances). In Tibetan this is called, Dri Zab, which means eating the smell. These offerings are made for the four guests but in particular, beings in the bardo (transition state); these are formless beings that do not recognize they are dead. Through the smell their five senses are fulfilled which can lead to liberation. These offerings are made to relieve the sufferings of these beings and are accompanied by prayers of aspiration for their wellbeing and enlightenment.
Traditionally these offerings are made in the evening.