Rather then look surprised or distressed, Ivar instead looks impressed when the knife goes sailing over his shoulder. He's got enough sense not to try and pluck a moving blade out of the air. People who did that were either fools or madmen. Despite how he came off, Ivar wasn't that insane.

He laughs for a moment. "Oho! You have been holding out on me! Where did you learn to throw knives?" Had he known that, he might have asked to see that skill from Jim rather then making him use the spear at first.