The knotgrass, healthy and bright, springs back into place once Imogen's hand has passed over it. This close to the caravan, she can see inside the windows. Despite the bright light spilling out, everything within is strangely muted and washed out, including the rest of the Pletcher family. Merlin's three brothers and two additional sisters and his mother, who stands frozen in the task tidying up the small kitchen.

So where is that light coming from? The source is not in Imogen's line of sight.