Crawling

Crawling is a feature that prevents the player from suffocating when inside small gaps. Crawling covers a pose which occurs when the player is in an area less than 1.5 blocks high.

Entering crawling
$$, it is only possible to enter crawling by exiting swimming mode in a one-block-high space, resulting in a glitched animation You can do this in Legacy Console edition too, but only if you keep sprinting.

$$, crawling can be initiated in any way that causes the player's head to intersect a block in such a way that the area underneath the block is less than 1.5 blocks. For example:


 * Closing a trapdoor on the player
 * Closing a fence when it is at the same altitude as the player's head
 * Using a piston to push a block into the player
 * Exiting swimming mode in a one-block-high space
 * Exiting elytra mode in a one-block-high space
 * Having a tree grow over a player
 * Having a shulker box push you down
 * This normally makes the player sneak instead of crawl, but when it is above a slab or a not-full block, then the player crawls.
 * Getting off a pig with a saddle if it's under a one-block-high space
 * Having a boat land on your head. Honey blocks make this easier to replicate

In these circumstances, the player automatically switches to a crawling state. When enough space opens up above the player's head, the player automatically exits this state and begins standing again. When crawling, the player travels slower than normal. The sneaking state gives the player identical dimensions to standing. In the crawling form, the player is reduced to 0.625 blocks tall, or $5/8$ of a block, meaning that they can crawl over blocks 0.375 blocks tall, or $3/8$ blocks tall, the height of a daylight sensor.

Trivia

 * Crawling was known simply as suffocation prevention as the technical behavior implied that before the crawling name was official.