It doesn't help since everyon else is so dour, but Coanacoch lets out a laugh before he can stop himself. He doesn't see Master Caramip as showing off, but rather as having a little fun. The slash without nails doesn't make nearly as much sense as a gouge, so it looks entirely impractical ... only further reinforcing his belief that she is just trying to get us to lighten up. Oh, well.
At the end of it (and his sister's request for provisions), he says, "Thank you, Master Caramip, it is an honor. If it would please the good master, I've been working on a maneuver and I wanted to show it to you to get your thoughts."