The Holes Walkthrough

1st screen:
On the left wall, Most Left hole at the bottom
On the left wall, on the right, third one from the top

2nd screen (click to the right):
Left wall, in the middle at the bottom
3rd screen (click to the right):
Left wall, most left hole at the bottom there's a piece of paper
Left wall, third from the left, at the bottom

4th screen (click to the right):
Left wall, in the middle, the 3rd one from the top.

Source: Escape Games 24