Regenerator parts. Some parts, imo, are scarier than the others though :X
Especially on Pro Mode D:
One part was the first time you meet the iron maiden, I think it was in this lab of some sort. Another part, on pro mode, is the first? time you see a regenerator, the one in the freezer room; the freezer room is already scary, but when you go out, there's like 1 or 2 waiting for you outside O_O
That's cause I didn't kill the one in the freezer first though xD; and cause I didn't have the rifle scope before I went to the freezer room ._.;
Also, the part where you first meet the insects, that place freaks me out ever since it spat and melted leon's face x_x;