Coin slot piercings are tongue piercings that are placed on the underside of the tongue, near the very back. The placement of these piercings is in a way that allows for a coin to be able to be inserted into the piercing hole on the tongue. As with all tongue piercings, there is a risk of infection and damage to teeth due to the use of jewelry. The coin slot piercing is a very rare variant of tongue piercings and is considered not to be very safe because it can cause damage to teeth and gums.