Irish dance is very unusual in that the arms are not used in the dance style. Meanwhile the feet move very quickly underneath a still and held torso. I can't think of another dance form where half of the body is kept in check. There are many urban legends as to why the arms are not used in Irish dance. These range from the disapproval of the Catholic Church of too close of an embrace between dance partners, to villagers not wanting British soldiers to realize that Irish dance traditions were continuing under colonial rule. There are also more practical reasons however, these include the fact that Irish dance developed as a social past time within rural communities. Dancing was done in small village homes maybe at a hearthstone by the fire place or on top of a table top so visitors to the home could see. Dancing in a limited area contributed to the arms being kept down by the side and the focus being maintained primarily on the footwork. The advent of Irish dance competition turned the Gaelic revival of the 1890's also impacted arm movements in Irish dance. It's actually quite difficult to keep one's arms still while moving one's feet so quickly. I often compare it to sprinting without using one's arms. Being able to maintain a still and vertical carriage while moving the feet very quickly underneath is a sign of a dancer's skill and is awarded high marks in Irish dance competition. Today, this is probably the most common reason why the arms are not used in Irish dance.