taking a line for a walk

My son is doing his art GCSE this year (next year) so I have been encouraging him to do things slightly outside his comfort zone. The other day he brought a rock home from the beach and i asked him to draw it by using one continous line and to look at the rock all the time and not look a the paper. the resulting image is the one on the top right. I thought he made a great job of it and suggested he did some more which he did. The one top left is the small wooden playhouse in the garden and the one on the bottom is of his bedroom. I think these images are really great and I just thought you'd like to see. I love the way they can't immediately be identified but that each one is an interesting and artistic response to the subject.