Yucky 9 year old boy humor

Joshua got in the car from art class on Monday with a mischievous, smug look on his face. For such a quiet little guy he has such an enormous amount of facial expressions that I didn't think too much about it. And then he said, "Mom, it might not be okay." Oh dear. "What might not be okay, darling?" "Well, you might not like my art from class," he replied. "Of course I will", I assure him thinking he is just feeling insecure. "What did you make?" He tries not to grin, not sure if I will see his humor and whispers, "Well, poop...but you can call it cow poop if that will make a difference." "No, no, that won't make a difference, I am sure. What was the assignment?" (I am buying myself time here while I think this over and try to act reasonable.) "Well, we are studying proportions. I thought it would be funny to draw big buildings in a city, a little house, a little airplane, and a big piece of poop. You know, to compare proportions." He shows me the paper, and points to the gigantic display front and center. Oh my. "Well, what did your teacher say? Because really poop and gas are something you boys might laugh about on the playground, I get that, but do you really think you need to bring it into the classroom?" "Oh no Mom. I didn't put any in the classroom. That would be nasty! See, I just drew the poop on the paper. My teacher thought it was weird, but I didn't get in any trouble." Keeping a straight face, I again requested poop and gas not be draw, discussed, shown, bragged about, or in any way displayed in class. Agreement made. Of course, when he showed Andy there was all out laughter and amusement. At the dinner table. Even I had to bite my lip a little.