Every once in a while a movie grabs you, unsuspecting, and hustles its way into your heart. Jeremiah Zagar’s “We the Animals” does that. This exquisite debut feature, based on a poetic debut novel by Justin Torres, is a tumbling evocation of a volatile family, narrated by one of three young brothers living in upstate New York with their Puerto Rican father and white mother. “Body heat!” the boys like to chant as they huddle beneath a blanket in the bedroom they share, and the warmth of their sibling furnace is almost palpable. They are the animals, incompletely domesticated in an adult world. They take love from their...