If the player tries to sprint at Swift before he dies, he says "Back the fuck up", done to prevent the player from getting past Swift and saving him.
On the Wii version, however, the player can easily get past Swift. They will see that the Vietcong is not standing there. However, he has spawned, as the player can see his hand sticking out of the cave wall. When the trigger is activated, the Vietcong will dash through the cave wall and stab Swift.
After Mason sees Reznov in the rat tunnel and speaks to him, Swift says "What the fuck is wrong with you? You need to get your shit together, now.", indicating that Mason is hallucinating Reznov's presence.