    static void
    postStepRemove(cpSpace *space, cpShape *shape, void *unused)
    {
      cpSpaceRemoveBody(space, shape->body);
      cpBodyFree(shape->body);

      cpSpaceRemoveShape(space, shape);
      cpShapeFree(shape);
    }

    static int
    begin(cpArbiter *arb, cpSpace *space, void *unused)
    {
      // Get the cpShapes involved in the collision
      // The order will be the same as you defined in the handler definition
      // a->collision_type will be BULLET_TYPE and b->collision_type will be MONSTER_TYPE
      CP_ARBITER_GET_SHAPES(arb, a, b);

      // The macro expands exactly as if you had typed this:
      // cpShape *a, *b; cpArbiterGetShapes(arb, &a, &b);

      // Add a post step callback to safely remove the body and shape from the space.
      // Calling cpSpaceRemove*() directly from a collision handler callback can cause crashes.
      cpSpaceAddPostStepCallback(space, (cpPostStepFunc)postStepRemove, b, NULL);

      // The object is dead, don’t process the collision further
      return 0;
    }

    #define BULLET_TYPE 1
    #define MONSTER_TYPE 2

    // Define a collision handler for bullets and monsters
    // Kill the monster by removing it’s shape and body from the space as soon as it’s hit by a bullet
    cpSpaceAddCollisionHandler(space, BULLET_TYPE, MONSTER_TYPE, begin, NULL, NULL, NULL, NULL);