How does an entity define a trap?

Okay, forum. Let someone help me with at least such an “easy” question, please...))

I made a block 3 pixels high (the top of the block, kind of like a trapdor)
Its function is to break when stepped on so that the monster falls into a pit with spikes.

As you understand, the monster simply runs around the pit covered with such blocks.

Initially the block was “transparent” (there were decorative holes in the texture)
Now I redid everything and made a “solid” block, but the monster still sees the hole.

Which option controls the block property that allows entities to see through them?