If something happens after something else, it will ensue, meaning it will follow after or be the result. When a sneeze comes out, and he hears the "Achoo!," a "Bless you" or "Gesundheit" soon will ensue.
One way to remember the verb ensue is to rhyme it with "due." A happening that is due to happen will ensue, "Throwing a glass of ice water in his face guaranteed that a chase would ensue." Often what follows is a response to words or actions, so what will ensue is what will happen as a consequence. A struggle might ensue if a thief grabs a purse, and a discussion might ensue if two sides disagree.