Watching a car crash, train wreck, or other such accident triggers the human fight or flight instinct. It’s why we can’t look away from flashing lights on the highway as tow trucks and emergency vehicles drag away wreckage and tend to the wounded. Looking away goes against programmed behavior. Audiences tuning in to HBO’s four-part miniseries “Allen v. Farrow,” directed by Kirby Dick and Amy Ziering, won’t look away, either, but not because they’re watching a train wreck; that metaphor does a great disservice to the series’ nauseating effect. Rather, they’re watching a woman’s tragedy in motion, as retold by Dylan and Mia Farrow, their loved ones, and the authorities and experts who tried her case.