The expression on his face - at least for the moment - is much closer to the look he gets when he's annoyed, mouth tugging off to one side and staying there as he looks back down at her.

"It's not stupid. I don't want you getting hurt if something goes wrong, though."

Which should answer the part about it being dangerous, although as long as he's careful it shouldn't be - and with a sigh, he lets the vexed expression go, and lifts the hand with the shard, pointing it at the training dummy.

"Look, just don't step in front at me for a few seconds. Can you promise me that much?"