In Chapter 4, Section 5, before you descend the staircase from the room with the two ammo boxes, there will be a large container. Shoot or hit it open to reveal a toaster with two pieces of bread in it. Press X and Marcus will pull the toaster and the pieces of toast will go in. Wait a few seconds and black smoke will arise from the toaster, then the toast will pop back out and triggers a hilarious moment with Marcus and Dom
[After toast pops up]
Marcus: WHO WANTS TOAST!?
Dom: I like em crispy!
Marcus: I like em crispy on the outside...
Dom: HELL YEAH!
(Note: Sometimes the second half dialogue will not be spoken if Marcus is aiming his weapon or is moving around. So be still and do not aim your weapon for your best chance to hear the whole dialogue.)