The four legged mannequins...

[The Dogfather]

Do you think the fact that they are hiding behind pillars and crouching by tables as if to imitate objects and furniture are actually doing that to hide from Pyramid Head and when they see it's just you they jumpscare or ambush you?

[JocularJosh]

Could be.
I also think it might be cause of James' sexual frustration. I mean they exist because of that, so in a way that he sees them as objects which is why they try to blend it and act as if they were simple objects.

[The Dogfather]

Those stupid four legged mannequins have jump scared me so many times even while I am trying to be aware of them

[Shaelent]

"The appearance of this delusion that comes after Lying Figure is far from human being, b/c James still keeps refusing to remember what he did or who it is. But it comes to be related to a disease. The looks of the upper legs came from a medical device for leg." - Masahiro Ito via Twitter

So yeah I'd be convinced since Pyramid Head is trying to remove the visions of them, the Nurses and other such monsters to make James face reality.

[V I D A L]

No. They are literally hiding from you in order to ambush you.
They are not always already in hiding. There are multiple times in which they are patrolling and the moment they see you, they run away to hide.

There was a time one of them even ran away to hide after I shot her. But she was too far away to risk charging at me, so she hid instead.