Pray ring the bell.

My hands are occupied." Rudolf's hands were indeed occupied; one held Bauer's arm, now no longer with a friendly pressure, but with a grip of iron; in the other the captive saw the revolver that had till now lain hidden.
"You see ?" asked Rudolf pleasantly.

"You must ring for me, mustn't you?
It would startle them if I roused them with a shot." A motion of the barrel told Bauer the direction which the shot would take.
"There's no bell," said Bauer sullenly.
"Ah, then you knock ?" "I suppose so." "In any particular way, my friend ?" "I don't know," growled Bauer.
"Nor I.Can't you guess ?" "No, I know nothing of it." "Well, we must try.

You knock, and--Listen, my lad.

You must guess right.