Line. The most basic element of art is line, and if you look at a painting by Van Gogh, you will see that he used dabs and strokes of paint to show emotion and movement.
I would paint my friends cause they,matter more to me.
Hope this helps :)
Answer:
Im not fully sure, but I think that it is a drawing by leonardo da vinci, and it was one of his ideas for a thing kind of like a helicopter.