“The doorbell rang several times a day, which was the cue for Sirius’s mother to start shrieking again, and for Harry and the others to attempt to eavesdrop on the visitor, though they gleaned very little from the brief glimpses and snatches of conversation they were able to sneak before Mrs Weasley recalled them to their tasks. Snape flitted in and out of the house several times more, though to Harry’s relief they never came face to face; Harry also caught sight of his Transfiguration teacher Professor McGonagall, looking very odd in a Muggle dress and coat, and she also seemed too busy to linger. Sometimes, however, the visitors stayed to help.”
―
J.K. Rowling,
Harry Potter and the Order of the Phoenix