'93 Corolla - Engine Knock

My son let the engine on the corolla run out of oil.. Now it is knocking. I'm familiar with standard engines with push rods etc.. But my question is when an engine like this loses oil what is causing the knocking. Lifters? Haven't had time to crack it open yet. Thought i would get a little advice first :)

What would be the first thing that would need to be replaced?


Virgin post btw.. :)