They can see how the shape bends! It doesn't show more detail than any of their shadowy self, but that still engrosses them into wiggling and curling the limb a lot.

The Knight is watching near as careful as Lemm when the glass is offered. They can hold it, but not take it, they warn. They don't know if they will, but knowing their own impulses, they figure it's better to be safe.

Greenhorn neither confirms or denies having this idea. They just pick it up in two tendrils' grasp and aim it towards the first fascinating thing around them--which is, naturally, Lemm. Lemm and his funny beard.