powers-of-observation

...[She] was not nearly so intrusive. If she happened to observe the comings and goings of her friends out of the corner of her eye (which she could hardly fail to do, given the nature of her favorite sitting-place) and chanced to be able to remember when she had seen them and where they had been going, it was simply a tribute to her keen powers of observation and recall. Conscious spying was beneath her altogether.