Text from wikipedia
Celebration in Thailand
Tongue slashing in Phuket
In Thailand, this festival is called Tesagan Gin Je เทศกาลกินเจ, the Vegetarian Festival. It is celebrated throughout the entire country, but the festivities are at their height in Phuket, where about 35% of the population is Thai Chinese. It attracts crowds of spectators because of many of the unusual religious rituals that are performed.
In accordance with the traditions, many religious devotees will perform ritualized mutilation upon themselves and one another (with the consent of, context and understanding of all involved and the practice itself) while under a trance-like state, including but not limited to: impaling through cheeks, arms, face, legs, back etc., with everything from as small as syringes to as large as is agreed upon between all members; partial skinning (the skin is not removed, just cut and flipped over); slashing of limbs, chest, stomach and especially tongue with swords, axes and knives; bloodletting; removal of tissue (normally limited to cysts) and intentionally wrapping or standing near fire crackers as they are lit.
This is done without anesthetic, always inside or near the temples surrounded by other devotees with only iodine, petroleum jelly and surgical gloves as precautionary measures. Despite this scenario, many of the same people performing the rituals are also the people who will care for many of the people in their recovery. The actual impaling is done by doctors and physicians in the community, is planned out for weeks if not months in advance and medical teams are present in and around temple grounds for the entire time of the festival, with spectators frequently needing more help than the devotees, who remain in a trance during this process and are monitored through the entire event in case they should drop out of concentration, in which case they are immediately take to medical professionals regardless of the circumstances to minimize post trance bleeding.
To this effect few people ever need to have prolonged medical treatment, and although in the weeks after the festival many people will be seen covered in bandages, scarring is uncommon, stitching, even on individual devotees who impale their cheeks, is rare, and return to daily activity for the devotees occurs shortly after the completion of the ritual, frequently before the festival ends unless performed on the last days, much sooner than before the bandages themselves are removed.
The purpose of this practice is a mixture of veneration for their gods and ancestors, to display their devotion to their beliefs and the trance itself, which although anecdotal in nature to what is experienced, has a profound impact upon demeanour for days or weeks after, frequently with devotees appearing exceptionally calm and focused in their day-to-day activities after the festival is completed.