Left image: The image shows a label saying "BUY 2 GET 1 FREE" which means that on a purchase of two unit of this product, the buyer would get one more unit for free.
Right image: The image shows two units of a product that is labelled "BUY 2 GET 1 FREE".
The image is funny because while there is an offer that lets the buyer have a free item if they buy two items of the product, there is only two units left which means that the buyer won't get the free unit.