The worst nurse

SIR HERBERT: Nurse!
COLONEL BURTON: Nurse! I'm thirsty!
SIR HERBERT: Nurse! My head hurts!
COLONEL BURTON: Nurse Sherman always wears such dirty shirts.
SIR HERBERT: He never arrives at work early.
COLONEL BURTON: He and …er … Nurse Turner weren't at work on Thursday, were they?
SIR HERBERT: No, they weren't.
COLONEL BURTON:Nurse Sherman is the worst nurse in the ward, isn't he, Sir Herbert?
SIR HERBERT: No, he isn't, Colonel Burton. He's the worst nurse in the world!