In the silence that followed, a dark flush stained the tan of Corporal's face

In the silence that followed, a dark flush stained the tan of Corporal’s face. “Here”, he said at last, “you give this lecture”. As if afraid to say any more, he tossed the grenade to the Professor. Quite unabashed, Private Quelch climbed to his ’ feet and with the air of a man coming into his birth-right gave us an unexceptionable lecture on the’grenade.
(a) Why did the Corporal ask Private Quelch to give the lecture?
(b) Why was there a silence?
© What does the word ‘stained’ mean?

(a) Private Quelch interrupted the Corporal twice in between his lecture on grenades. In order to save himself from embarrassment, the Corporal . asked Private Quelch to give the lecture.
(b) There was complete silence because the lecture had been interrupted for the second time by the Professor and so the soldiers were scared of the reaction of the Corporal.
© ‘Stained’ means to change the colour or, discolour something.