In the very last scene in New Zealand when Jordan is giving a motivational speech, he approaches his first target in the audience and says 'Sell me this pen.' As he does so, he holds out a pen in his right hand. When we cut to the shot to the person's face, we see that the pen is in Jordan's left hand; this goes on and on with every person.
The humming chant Matthew McConaughey does and Leonardo DiCaprio adopts is actually something McConaughey does before scenes to relax himself and clear his head. He did it before shooting the scene with DiCaprio in the restaurant, and after a few takes DiCaprio suggested that it was put in the scene, so it stayed.