What uncharacteristically foolish thing did Rab do? What was the result?

Rab becomes fascinated with the British officers’ muskets. He dreams of having one for himself. One day, Rab accidentally touches an extra musket while explaining to Johnny how it works. A British lieutenant sees him and hits him hard in the head with the side of his sword. Rab is knocked unconscious, but a sympathetic British medical officer helps Rab.