The brothers used them, along with newspaper, cardboard and poster paint, to construct a series of gory dinosaurs for their most recent exhibition in Liverpool.
Commentators noted that the pieces appeared to have a primary-school quality to them, which was probably deliberate - the artists have poked fun at the education system before by sitting art GCSE in 1999 and doing just two weeks' work (they both got B grades).
Now the brothers are helping Thornhill primary in Islington, London, raise money to build an arts block. They have donated a sketch, which the school will auction tonight, along with an England football shirt and a signed photo of Kate Moss. Other PTAs have reason to feel jealous.