The answers came quickly, and they were uniform in their calm: this is what some birds do, and it is not personal, or rather it is very personal, but only to the bird. Blackbirds do it when they have chicks. Crows do it when they have a grievance, and crows, famously, hold grievances across time and across individuals — a single crow can tutor the rest of its murder in the particulars of a specific human face, which is either impressive or alarming depending on your relationship with the birds on your block.

The Embarcadero stretch near the Ferry Building has enough mature plantings and decorative ironwork to make decent nesting territory, and nesting season has a way of reorganizing who has priority on a given corridor. A red-tailed hawk with a nest along a tree-lined road, one commenter noted from experience, can run a harassment campaign against pedestrians for months. Hawks have talons built for catching things that don't want to be caught.

The folk remedy for corvid attacks — suggested by at least one thread participant — is to put eyes on the back of your hat, a technique borrowed from runners in cities with aggressive magpie populations. Whether this works on Bay Area crows is, as yet, uncontrolled data.

Someone else noted that the Stanford Theatre happened to be screening The Birds that same evening, which the algorithm of city life occasionally arranges just to see if you're paying attention.

Anyone walking the waterfront in the next few weeks should look up when the path passes under a dense canopy. The bird that hit someone last week is probably still there, watching the same stretch of pavement, with the same assessment of threats.