It's clearly designed... or not

Proponents of Intelligent Design (ID) claim that we can infer design. That is, they split the world into two categories of objects: those that were designed by something intelligent, and those that were not. And they claim that we can tell the difference.

Well, was this designed or not? ...



It's the famous neanderthal bone flute. Some say that a neanderthal created it purposefully for making music (intelligent cause). Others say that the holes were made by the teeth of a hungry animal (non-intelligent cause).

If it's as easy and clear-cut as IDers claim, then why is there so much controversy?