From J Gilbert's website:   Q: Is there a story behind the squirrel and grapes motif?   A: I don't know of any textual reference, but squirrel and grapes is a very common kodogu motif. People in the US often mistake the squirrel for a fox. I can understand that, since Aesop’s fable of the fox and grapes is more familiar in the West.   The squirrel and grapes motif probably entered Japan in the Nara period by way of Tang China via the silk road. It may have originated in Greece. It’s a