Throughout the game, the majority of the people talking on the cross-com will just move their mouths up and down when talking - this becomes evident when they are no longer speaking, but their mouths continue moving.
When the helicopter is taking off with you in it on the mission (where the U.S. embassy gets bombed and you have to hold off the enemy until reinforcements arrive) it is flying up and you can't see the helicopter's reflection in the building's windows (which are mirror-like).
Throughout the game, when you are riding in the helicopter, sometimes the helicopter's blade's shadow will not be turning on the ground as it actually is.