A big what???

This morning after we finished our shower, my son was sitting on the floor wrapped in a towel. As I turned around to get a towel for myself, my son saw my 9 month figure & said, "Woah... Big butt!" I couldn't help but laugh out loud for several minutes which made it even funnier for him & he had to say it again. When Daddy heard what he said, he also burst out laughing & then added, "Son, you never say that to a woman." (LOL)