My treasure

So I was standing in front of a class last week listening to the JTE explain english grammar rules in Japanese when he turns to me and asks if I've learned any interesting Japanese. The best thing I could come up with is that I know how to write "sushi" in Kanji. So I turn to the board and wrote it impressing the students to no end. And, ever since my self-introduction, students give me "the horns" for almost any occassion so a few students put their horns up, but they had their thumbs out. So I corrected them, and then went on to explain what a longhorn is. So, I started drawing a Texas Longhorn on the board and a student said something and everyone laughed. The teacher explained that they were laughing because my drawing, thus far, looks like "your treasure" and, with both hands, pointed at his crotch.
Through a laugh I tried to explain that it was a kind of cow and a student called out "bull!" "Yes" i said, "very good" and I wrote "bull" under the Texas Longhorn. Again, the class laughed and the teacher turns to me and says, "They're wondering how big your treasure is." The class goes silent in anticipation of my answer. There's a long akward pause. "Well" i say while pointing at the board, "like a bull's."
Some students laughed and others put up their horns.