They had to x-ray them to tell the difference?
Check it out:

A Mexican drug cartel recently used its painting skills to smuggle millions of dollars of marijuana into the United States, a brushstroke of genius of sorts until the effort was uncovered by a federal border agent.

U.S. Customs and Border Protection (CBP) agents stopped a suspicious tractor trailer late Thursday on Interstate 19, south of Tucson, Ariz. Inside, the driver said, was a shipment of watermelons. But when agents inspected the shipment using X-ray imaging, they discovered the purported fruit was actually packages of marijuana painted to look like watermelons.