Commentary Par I 85-87

We learn definitively that Beatrice truly reads the protagonist's mind, a capacity that Virgil at times claimed, but was rarely, if ever, capable of demonstrating (see C.Inf.XVI.115-123; C.Inf.XXIII.25-30; C.Purg.XV.133-135).  Her lips open in response before Dante's question has been voiced.

The reason for the agitation experienced by the protagonist is explained by verses 82-84.