When we first discussed mistakes in "The Lord of the Rings" earlier on in this list, we said we were prepared to cut them some slack because all three films were epic length and shot back to back. We'd probably draw the line at this many mistakes though. Another error in another battle scene. Here, we have an ax that's been used in battle, and has the scuffs and bloodstains to prove it. Or, at least, it did. Blink and look back, and it's all gone.
Now, it's possible he wiped a cloth on it, but that wouldn't explain the shine of the cleaned blade. We also accept that he may have wiped it on his beard, but that's a little disgusting and wouldn't have got it even close to being that clean so quickly. It looks like it's never seen action.