Toilet Factory

Yesterday at dinner Sam started telling me about his day at school.
"And guess what?  I painted a painting!" he exclaimed.
"Oh, you did?" I asked.
"Yes.  A painting of a toilet factory," he told me.
"A what?"
"A toilet factory," he repeated.
I thought about how to respond to this appropriately.
"Why?" I asked, trying to figure out whether he was doing it to make his friends laugh.
"Because I wanted to," he replied.
"Did your teacher want you to?" I asked.
"I don't know," he shrugged.
"Well it seems like a strange thing to paint."
"No, it's what I wanted to paint."
"Did your teacher like it?" I asked him.
"Oh yes," he told me.  "And mom the good news is that it's for the art show, which is the same day as my birthday!"
I tried not to choke on my coffee, "great!"
He leaned forward and whispered, "I didn't tell my teacher what the painting was of."
"Good plan," I whispered back.  "It can be our secret.  We won't tell anyone at the art show either."