and let 's not forget the time ( just three days ago ) when he followed her into the kitchen and she was n't there she 'd turned out to be behind him , coming down the stairs , and how she had done that seems less important to him than why she had done it , gone sneaking up the back stairs and then come tromping down the front ones ( because that is what she must have done ; it 's the only solution he can think of ) .