‘The rat,’ said O’Brien, behaving as if he were addressing an audience, ‘… is carnivorous… “
This didn’t need to be said, but O’Brien said it as part of his need to terrify Winston Smith, whom he has bound to a chair.
O’Brien goes on to describes rat attacks in poor neighbourhoods announcing how one could not leave a baby alone for five minutes. He describes how the rats would eat the baby. He goes on to describe how rats attack sick or dying people. And, then, directed at Winston;
” They show astonishing intelligence in knowing when a human being is helpless.’
At that point the rats squeal as they tried to get at each other through the partition in the cage.