Essential oils expressed from citrus peel over the top of a drink. Either by cutting the fruit with a canelle knife over the top of the drink. or by pinching a rectangular slice of peel, again over the top of the drink. Either way, the name of the game is to express the oils from the peel over the drink to deliver a powerful aroma. The peel is usually then fashioned into an attractive shape and added to the glass for visual impact.