R was digging up a pavement and laid a punner-hammer across the entrance to that section to prevent people walking onto that section of the pavement. A blind man walked onto that area, having missed the punner hammer and fell, leaving him deaf. HL said that R had a duty of care to all pedestrians to warn them about going onto the area, including blind pedestrians. R would have been entitled to assume that a blind person would take reasonable care of themselves e.g. by using a stick (i.e. if they had put up a proper barrier that the stick would touch then they would have discharged their responsibilities).
Lord Reid: In determining what is reasonably foreseeable, some “common knowledge” has to be assumed e.g. that blind people exist and walk on pavements (even if R did not foresee a blind person walking along at the brief period where the pavement was left dug up).