A moving leg gets something.
Note: You will never get anything accomplished (like mastering ‘an Ghaeilge’) by just sitting around thinking about it. Active people reap the benefits of their exertions.
Note also: The Irish language has terms for parts and areas of the body which go nameless in other languages. That being said, it is curious that the word “cos” can refer to either the leg or the foot; and it is often used without really differentiating which portion of the appendage is in question.