While shamanic practices vary greatly between cultures, one of the more unique traditions has to be found in San Juan Chamula, Mexico. The Tzotzil, a local indigenous people, frequently drink Coca-Cola or other carbonated beverages in the belief that the burps caused by the carbonation help expel evil spirits and illnesses. Some shamans in the area include drinking Coca-Cola in their healing rituals.
It is unclear where this belief originated, but one theory centers on the relief that soda can give for an upset stomach. Burping is a very visible and immediate side effect, so when the sick person burped and felt better, those attending him or her may have attributed the end of the sickness to the burp itself. Or, as Shrek the animated ogre would say, "Better out than in."
Interesting facts about belching: