Spring of Trivia | graffiti in text books

My wife just sent me this clip (2004) from Toribia no Izumi, also known in its reincarnated life on Spike TV as Hey! Spring of Trivia. A research team scoured through 10,000 middle school textbooks (from several areas of study including history, science and music) and aggregated the graffiti/doodles into different categories.  The clip (Japanese only) is highly entertaining but for those of you who don’t care to watch, here are the top 3:
#3 – glasses and/or sunglasses
#2 – beards
#1 – speech bubbles

In each case prime victims appeared to be historical figures, but popular artwork and sculpture were not spared. I was surprised that poop, given that it is disproportionately easy to render versus comical effect, was not higher on the list.  It was 25th.

It would be really interesting to compare with a similar study conducted in the States. Any volunteers?