In my previous post, I neglected to mention the little story about Charles Rosen that David Carter, Elliott's son, told me when I spoke with him at Tanglewood in 2008. Like me, David has been an avid fan of the Marx Brothers ever since he was a teenager. Once, in the 1950s, not long after Rosen and Elliott Carter had made each other's acquaintance, Carter brought Rosen home and, for some reason, left him alone with David for a little while. An awkward silence ensued, and, to break it, David asked Rosen if he could play stunt piano like Chico Marx.
It turned out Rosen could, and he kept David entertained, shooting the keys, etc., until Elliott came back into the room.
Davis said he was 13 or 14 when this occurred, but Rosen himself has said that he did not meet Elliott Carter until 1956, which would have made David 15 or 16.