Original artwork, not a still
Not a Drum was Heard (unpublished radio play, 1959)
Henry has always led what could be called a sedentary life, if only he'd every got as far as actually sitting up.
Behind the line
What it means
Our interpretation.
Henry's life is described as falling short even of sitting up. The joke stretches the idea of a sedentary existence until sitting becomes an achievement rather than ordinary inactivity. That reversal gives the sentence its dry humour, making a restrained description carry an extravagant exaggeration.
Context reviewed