This can be achieved easily at the start of the second chapter,
Stockyards.
Just after passing the first movement sensors, you'll see a door that is the entrance of the first secret area of this level. Enter it with
and you'll be in a walkway at the back of the screen. Open the bird portal at the end of the walkway (
+
) and enter it.
You'll be in a platform and a Scrab will be below. When it is under the platform that you're standing in, jump to the right and run to the end. Go up the platform there, and achievement unlocked.
Video of the method follows: