The torture in this section is mental. We gain an insight into the mind of Winston Smith, an average man living under the Regime.
He has been physically and mentally tortured.
There is no reason for it. That is the key feature. The meaninglessness of torturing a man who is no one in particular, who did nothing, and knows nothing.
His mental challenges, trying to figure out what ‘reality’ is, what he should think, how he should view society is painful.
And his failure to become a complete mindless sheep has him sent to the terrifying Room 101.