"Everyone wants a panda!" said Kathleen Buckingham, the lead author of a recent paper on panda diplomacy. "But China can't just start giving them to everyone; otherwise, they lose their charm, don't they? They wouldn't be rare."

So how does a country get some pandas? For starters, it helps if a nation has something China is interested in, such as advanced technology or natural resources. (Bonus points if you have both.) Recent panda loans have coincided with deals to supply uranium -- a fuel for nuclear energy -- foreign food and drink, and renewable energy technology.

A recently inked loan to Belgium is for 15 years, likely a record as far as panda loans go, Buckingham said. Belgium is now China's sixth-largest trading partner in the E.U., and bilateral trade grew to $26.3 billion in 2012.