A childhood belief about sex

When I was around 10 my mother walked in on me mastrubating and let out a loud gasp. She ran out of the room and I, not sure what had upset her, went after her because I was worried. She proceeded to give me a long lecuture about the fact that "mastrubation" was perfectly natural, saying that she was glad I was mastrubating because it meant I was normal...I kept wondering why she was talking to me about this.
it wasn't until 20 minuites into the discussion that I figured out the "mastrubation" was the word for what I had been doing.
Before then I thought mastrubation was called "riding" and that it was called that because you were boucing up and down like you were riding a horse. Natuarally, I thought that's why people liked horses so much, and why women were always dreaming about riding off on a white horse with their knight in shining armor.