Question on ENABLE_IMPACT

// The following example shows how to use events for an object that flies ahead until it collides with a block or entity.
// The event function then plays a collision sound and lets the object ricochet from the surface. 


function bounce_event() 
{
  switch (event_type)
  {
    case EVENT_BLOCK:
      ent_playsound(my,whamm,50);   
      vec_to_angle(my.pan,bounce); // change direction
      return;
    case EVENT_ENTITY: 
      ent_playsound(my,boingg,50);  // play a different sound
      vec_to_angle(my.pan,bounce); // change direction
      return;
  }
}  

action bounceball() 
{
  my.emask |= (ENABLE_BLOCK | ENABLE_ENTITY); // make entity sensitive for block and entity collision
  my.event = bounce_event;
  while(1)
  {
    c_move(me,vector(5*time_step,0,0),nullvector,0); // move ahead until obstacle is hit
    wait(1);
  }
}