I think it would be 'After drumming on his desk, Stewart was disciplined by Mrs. Hobson for distracting students from their exams.'
The answer is: Impersonating and remaining silent.
In the passage, the narrator describes Tom Stoppard's play "Rosencrantz and Guildenstern Are Dead." Both originally Shakespearean characters from "Hamlet," Stoppard develops them further in their own play, in which they "pass the time by impersonating other characters" and "remaining silent for long periods of time."
