the Headmaster's anteroom: a boy taking his own injury's vital signs
Hal had been flexing the ankle and watching the swelling shift slightly under the multiple socks. He stood and put his weight on the ankle experimentally a couple times and then sat back down and flexed it, watching the swelling very intently.
Context
Hal monitors his ankle the way a mechanic checks a bearing — "flexing the ankle and watching the swelling shift slightly under the multiple socks," loading it "experimentally a couple times," reading the swelling "very intently." The injured joint has become an instrument he consults, a live gauge he can't stop watching. This is what it is to inhabit the body-as-machine: even at rest you're running diagnostics on the part that's failing.