A cocktail shaker is a metal container used to mix cocktails by shaking their ingredients vigorously with ice. The classic cobbler shaker has three parts, tin, cap, and strainer, while professionals favour the two-piece Boston shaker with a separate strainer. Shaking chills, dilutes, and aerates the drink, giving a frosty, well-blended result suited to cocktails containing juice, cream, or egg white; spirits-only drinks are typically stirred for a silkier texture. Technique matters: a hard, brief shake achieves proper chill without over-dilution. It is the iconic tool of the bar, as much theatre as equipment.