Shortly after meeting the long-armed monster in Little Nightmares for your first time, you will be put in a situation where you need to sneak around it. It isn't immediately obviously where you need to go. If you try walking past him, the wooden floor will make creaking noises and alert it to your presence. Meanwhile, the open wall space to his left appears to be the way to go, but is impossible to climb through.
The answer here is to stay close to the camera and walk across the carpeted rugs. You can then pass through a few cages before dashing through a door on the other side.
You will encounter this monster a few more times in the future. Note that it is unable to see you, and instead relies on noise to find you. This allow you to position yourself in ways that may appear dangerous, but are in-fact safe.