Halfway through “28 Years Later,” our young hero, Spike (Alfie Williams) learns a new phrase: “Memento mori,” Latin for “remember death.” In a world bound by death – borders and culture defined by it – one would be hard-pressed to forget. But for Spike, just 13 years old, the phrase becomes a lesson that to honor death, even in a circumstance where death, dying and the undead are ubiquitous, is to honor life itself. Funerary rites serve a purpose: to celebrate life while we acknowledge death.