Sasuke himself picks a spot behind the dividing wall, waiting until Heiji has left to do a quick test without actually releasing the blade. As with kendo, there was the odd sensation of familiarity as he shifted into the stance, his grip on the blade immediately switching to a more comfortable one for throwing.

...And quickly went back to a neutral one, feeling vaguely disturbed as he allowed his grip on the knife to loosen. What a thing to know...

Once Heiji reenters the room, he's on the alert, the knife held low at his side for now. He's going to be sure the robot is in range before he even readies to throw, whether it puts him at a slight disadvantage or not.