Arthur is prone to nosebleeds. One is currently threatening to erupt, evidenced by the pink-tinged snot appearing from one nostril. Thus Arthur is currently sitting in a small armchair, "being quiet for a few minutes" until the threat seems to have receded. We will make no cynical observations as to just how long Mary might consider it necessary that the boy "be quiet". It's for his health and nasal security, after all.
Arthur sits in the small armchair with a book and a soft toy.
"I think," he suggests, veteran nose-bleeder that he is, "I might need a couple of kleenexses."
Which are duly provided.
"And a helmet."