Print Minecraft 1x1 block?

I saw that you can go through a 1x1 hole in Minecraft by crouching like this…

How does it work?

Press the duck button

In which version

On the PC with a mod or swimming.

1.16

You have to place a trap door where you stand next to and then fold the trap door down, causing you to lie down

I only know about swimming. You can swim through a 1x1 gap.

Hi, I saw that many answers here are nonsense.

You build two blocks next to you and then grab a trap door on the top so that it goes down. Then you stand in front of the trap door and close it. Finished. That with the blocks was purely to explain, the main thing is that the trap door is on the upper block and opens up. So you can build it anywhere.