How to Use a Dressing Room in Japan

I went to a Japanese department store and saw some clothes I wanted to try on.  In the center of the clothing department was a little dressing room with a curtain that you pulled once you stepped on the platform.  There was a mirror in the room and looked just like a dressing room you would see in the United States.  Once I was in the room, I heard this commotion.  There was a woman yelling at me.  I wasn't sure what she was saying so I just poked my head out from behind the curtain to see what she wanted.  She seemed distressed.  I then saw her pointing to my feet and saying "kutsu, kutsu".  I then realized she wanted me to take off my shoes before entering the dressing room.  She had a very infuriated look on her face, so I was sure to say in English, "I am sorry, what is the problem?"  She was taken aback as she was so sure I was Japanese and just being rude.  I told her I was American.  She instantly became kinder and then pointed for me to take off my shoes.  I apologized, took off my shoes and thought, I better remember that!