Wikipedia
MagiCans were special, mechanical cans used by Coca-Cola in the United States of America as a part of their $100-million "Magic Summer '90" promotion. The MagiCan promotion began on May 7, 1990 and ended on May 31.
In this promotion, some Coca-Cola cans had cash prizes or gift certificates inside instead of Coca-Cola. The prizes were spring-loaded to pop out once the can was opened, lifting the prize into the opening. The prize would either be money, from $1 to $500, or coupons redeemable for trips or merchandise. The total giveaway of cash and prize coupons was $4 million. The original plan was to randomly distribute about 750,000 MagiCans among the 200 million cans of Coca-Cola Classic in circulation at any one time. To make the cans feel and weigh normal, and prevent people from easily finding the prize cans, a sealed area within the cans was filled with a mixture of chlorinated water and foul-smelling ammonium sulfate to discourage drinking. Though initially a great success, leading to a rise in sales, technical difficulties led to the promotion's early termination.