From Who the Hell’s in It: Conversations with Hollywood’s Legendary Actors
Of course, he was like no other dancer: his straight-legged, cocky, constantly surprising way of hoofing — which is how he started in show business — was seen only in a couple of other films, not really very good ones. Footlight Parade (1933) is the best of these, yet his manner as an actor and his grace as a performer no doubt owe quite a lot to his dancing days. He just moved eloquently, and therefore could easily have been a great silent star. However, he arrived with the talkies, and gave even the least of them a large measure of his boundless panache.
I used to wonder at the unusual way of dancing, so unlike ballet or standard tap moves. Once I saw Irish dancing, I wondered no longer. He obviously learned his craft from that style.