Sneaking
Sneaking is part of the basic controls in Minetest for preventing falling off edges. This move is a bit unusual (and broken) in some aspects, so it deserves its own article.
Basic sneaking
The default key for sneaking is Shift. You will sneak as long as you hold down the sneak key. You can not sneak while you are at a ladder, inside a liquid or have activated fly mode.
Sneaking makes you walk slower and prevents you from walking and falling over a block's edge. If you try to walk beyond the edge of a cube while holding down the sneak key, you won't fall. You can walk a bit beyond the block's edge while sneaking, up to a certain limit, of course. This means for a spectator it will somewhat look like as if you float in mid-air while sneaking.
Sneaking can also help you walking at edges of ledges where you don't actually have enough space to stand on. An example is shown in the first screenshot.
Known bugs and weirdnesses
Avoiding fall damage
You don't suffer any fall damage if you fall on a normal block's edge or on a slab or snow or on some other non-cubic shapes while holding down the sneak key. This bug is known as issue 329.
Sneak glitch
The sneak glitch is a weird behaviour which makes it easily possible to quickly reach high places which would normally not be reachable by normal jumps in the same time.
The sneak glitch is considered to be a “bug that has become a feature” in Minetest and will probably not be fixed. This is intentional. However, it it is possible to disable the sneak gltich manually.
Climbing high blocks
Normally, you can only jump high enough to climb 1 block at once. But sometimes you can climb a wall of a height of 2 blocks while jumping and sneaking at the same time. This is not reliable and requires many attempts to actually climb the wall. This behaviour is considered to be part of the sneak glitch.
Sneak elevator
A common structure for using/abusing the sneak glitch is the so-called sneak elevator. A sneak elevator is a special alignment of blocks which are built in such a way that makes using the sneak glitch very easy and helps to climb it up in an instane speed. The second screenshot shows an example of a sneak elevator. Similar structures with the same function might exist.
To use/abuse the sneak glitch, stand at the corner of the sneak elevator, then hold both the sneak key and the jump key. You will move up the entire structure at an insane speed.
Disabling the sneak glitch
To disable the sneak glitch for a given world, simply activate the "Disable sneak glitch" mod and all weird behaviours caused by the sneak glitch (like using/abusing the sneak elevator) won't work anymore. Additionally, fall damage will behave normally.