Why that tiny piano........

........ at the Liszt concert? Seems unlikely that it would have been adequate for a theatre of that size. I know the sound was studio dubbed but still, for realistic visual, wouldn't it have made more sense to use a bigger concert piano for the scene? Or is it that the concert piano we know today didn't yet exist at that period? But they must have had a bigger piano then instead of what looks like a small upright for home practice. Is that a Pleyel piano that Bogarde pretended to be playing on?