Burrowing leeches can take a traveler by surprise quite easily. Their body is a single, long, muscular tube of sticky, mucous-secreting flesh covered in a thick, hairy layer of skin. They have only one orifice which they use for eating, drinking, defecating, and breathing (although leeches can last for multiple days without needing to breath, presumably oxygen is either produced internally or stored in the body for long-term use). Leeches are blind but can sense movement as their prey walk through swampy water. They slowly wriggle forward under the mud and their outer layer of skin pulls back to allow them to spread their inner jaws wider than a fully grown travelers waist...

Leeches erupt up from the ground catching their prey unaware and partially swallowing them. <3 Because of their slow speed, the initial ambush is the determining factor in whether or not a leech will have a successful hunt. A single gulp is all it takes to trap an unlucky victim within the leech's sticky jaws, although slamming prey into the muddy ground can help disorient it while the leech gets comfortable and secures their catch.

Once secured, the leech's thick skin prevents their prey from harming them during the struggle. The leech's entire upper body is a heavily muscular tube that can grip tightly onto prey, secreting thick, sticky saliva and lubricating fluids to help the prey slip down. Once a prey is captured, a leech will often fully emerge from the mud so that they can slowly slurp down their meal at their leisure~

This process can take anywhere from 1-15 minutes, largely determined by how hungry the leech is and how comfortable the above-ground climate is. If surprised or interrupted, a leech will quickly swallow its prey and immediately burrow, often in the space of seconds. If uninterrupted, the feeding process for a leech can be a long, drawn-out experience~

A leech's stomach is not a separate organ from its throat, so prey are merely pulled deeper into the leech's body until the leech is comfortable with their position. Every single inch of the leech's inner throat and stomach is muscle, giving the leech precise control over positioning, manipulating, squeezing, and restraining prey within its body throughout the entire digestion process~

Once a leech is finished swallowing its prey it expels excess air and any indigestible remains of previous victims that it may not have yet had the chance to release :3 Leech digestion is slow, but extremely efficient, capable of absorbing and utilizing almost every nutrient that it can digest. Bones, clothing, and hair often remains, reduced not into feces but a sticky pellet of indigestible material that can be vomited out or held within the stomach to digest further. It is theorized that rather than producing traditional waste the leech converts unusable byproducts of digestion into its saliva and lubrication. This is only theory though, it is possible that leeches produce more traditional waste but merely expel it deep underground, leaving their victims permanently entombed in the tunnels in which they died. 

Once a leech's feeding is done, the thick coarse layer of skin slides back over the leeches mouth, sealing it to a point. This ends the last sight of light or taste of outside air that the prey will ever experience for the rest of their short life, before the leech dives back into the ground, squeezing its prey as it compresses its body to fit both it and its new occupant~ into the soggy tunnel. Once fully submerged, the leech floods its throat and stomach with digestive enzimes and burrows deep within the ground where it is impossible for any rescue team or other predator to ever find it, then relaxes to leisurely digest its struggling victim <3

Leeches typically do not emerge back up from the ground until their prey is completely digested and is at least reduced to bones. Because of their bodily efficiency and slow, thorough metabolism, this process can take up to a full week depending on the size of their prey.

It is assumed that eventually prey would die of suffocation within the leech's body, if it didn't crush or drown them first. But because of the solitary feeding habits, no one is quite sure how long that process takes and how long the victim would remain conscious before the last remaining air in the stomach was exhausted >:3 Whether that is hours or days, the prey spend their remaining life deep beneath the ground, surrounded by clinging flesh that kneads and restrains them and tenderizes their flesh, basting them in the slow, thick digestive goo that is slowly softening their flesh. The prey must have the full knowledge at this point that they are surrounded not just by their predator but by meters and meters of dirt that will make it impossible for anyone or anything to hear or find them or notice their struggles :3 Any whimper of protest, and pained gasp for air or pointless struggle is completely lost to the void, unacknowledged even by their predator, smothered beneath uncaring dirt and mud as the wet stomach entombs them and the flesh continues undulate, endlessly and lewdly squelching around them >:3

Leeches are affectionate predators who (despite their simple biology) appear to derive pleasure from feeding and seem to enjoy manipulating and massaging and playing with their prey as they are swallowed.

It is reasonable to believe that this behavior would extend to digestion as well given that leeches stomachs possess the same muscular control as every other part of their body. But as of yet there is no way to confirm. Whatever the leech does during digestion, it is a private affair, shared only between itself and its victims. <3