Playing a guitar that has its marked frets removed, still produces the same sound as with them, T. The player knows where each note's sited, and where to strike. The result's the same whether marked or unmarked.
Probably because the player's deliberately missing striking behind the fret. It has no different sound at all, T. It's a stringed guitar with the fret marks missing. You can get the same sound from a guitar which has the frets visible. It depends on where you strike the notes.
It depends on the notes played, T. By using frets, the musician's keeping to a set pattern of music. Being fretless allows the instrument to hit notes not usually heard within our sort of music, but could be reproduced according to where the fingers hit the fret board.
Oh no I'm not, Watson. The reason it sounds different, is because standard western guitars stick to notes and pitches which we're used to. The frets're there as a guide, but strike away from these, and you'll get some different-sounding notes.
Well of course they sound different, because the first guy's playing at a higher octave and not hitting behind the frets - because there aren't any! You could play bass on both of them though and make them sound the same.