code: public void addAnimation (Animation anim, long delta, Runnable completionAction)
      {
          // sanity check
          if (_finished) {
              throw new IllegalStateException("Animation added to finished sequencer");
          }
  
          // if this guy is triggering on a previous animation, grab that
          // good fellow here
          AnimRecord trigger = null;
          if (delta == -1) {
              if (_queued.size() > 0) {
                  // if there are queued animations we want the most
                  // recently queued animation
                  trigger = _queued.get(_queued.size()-1);
              } else if (_running.size() > 0) {
                  // otherwise, if there are running animations, we want the
                  // last one in that list
                  trigger = _running.get(_running.size()-1);
              }
              // otherwise we have no trigger, we'll just start ASAP
          }
  
          AnimRecord arec = new AnimRecord(anim, delta, trigger, completionAction);
  //         Log.info("Queued " + arec + ".");
          _queued.add(arec);
      }
docs: Adds the supplied animation to the sequence with the given parameters. Note that care
  should be taken if this is called after the animation sequence has begun firing animations.
  Do not add new animations after the final animation in the sequence has been started or you
  run the risk of attempting to add an animation to the sequence after it thinks that it has
  finished (in which case this method will fail).
  
  @param anim the animation to be sequenced, or null if the completion action should be run
  immediately when this "animation" is ready to fired.
  @param delta the number of milliseconds following the <em>start</em> of the previous
  animation in the queue that this animation should be started; 0 if it should be started
  simultaneously with its predecessor in the queue; -1 if it should be started when its
  predecessor has completed.
  @param completionAction a runnable to be executed when this animation completes.