this is from wiki under different ways to shoplift.

Milkshake subterfuge

A less common shoplifting technique used for smaller high-dollar items is the milkshake subterfuge. A milkshake is purchased by the shoplifter and taken into the store. The shoplifter proceeds to drop small heavy items like jewelry into the milkshake. On leaving the store their milkshake is unlikely to be searched. Shoplifters using this method must be wary of drinking too much of their milkshake or the items will be revealed in the bottom of their cup.