Life lived inside the substrate
Most frogs sit on their substrate. A pacman frog lives in it. This heavy-bodied South American ambush hunter settles into the floor until only its eyes and the top of its broad head break the surface, and there it may sit for days, waiting for food to wander within range of a mouth that makes up much of its body. That means the substrate is not a floor covering for this species — it is the habitat itself, the hiding place, the humidity source and the hunting blind all at once. It also has to survive the pacman's feeding style: when prey comes close, the frog lunges with its entire mouth open and takes in whatever the prey is standing on. Safest here means deep, soft, fine-textured and damp, with nothing in it big or stringy enough to cause trouble on the way through.
Coconut fiber, at the right depth and dampness
Coconut fiber is the substrate pacman keepers settle on because it meets every part of that description. Its particles are small and soft, so the incidental mouthfuls that come with every lunge pass far more safely than bark or gravel would, and it holds water evenly through its whole depth. Lay it deep: an adult pacman needs enough fiber to bury itself completely, several inches across the enclosure, and juveniles need proportionate depth too, since a frog that cannot bury properly is a stressed frog. Keep the fiber damp throughout — the classic test is that it should feel like a wrung-out sponge, moist to the touch without dripping or pooling. Too dry, and a pacman responds as it would to a dry season, sealing itself in a thickened skin cocoon and refusing food; too wet and swampy, and the floor turns bacterial, which shows up on the frog's skin.
Feeding without a mouthful of floor
You cannot stop a pacman taking in some substrate — it is built into the hunting style — but you can cut the amount down. Offer food with long tongs, wiggling the prey just in front of the frog's face so the strike happens at the surface rather than through the floor, or present larger items on a shallow, smooth dish the frog can lunge over. What you must keep out is anything that does not behave like fiber: sphagnum moss in long strands is a genuine impaction risk because it tangles and does not break down, gravel and coarse bark are worse, and soil containing perlite or fertilizer granules adds white, swallowable lumps and chemicals to a floor the frog effectively eats from. Plain fiber, refreshed regularly, asks the frog's gut to deal only with small amounts of fine material it is equipped to pass.
Upkeep around a frog that will not move
A pacman picks a spot and fouls it, sitting in its own waste as the days pass, so maintenance works around the frog rather than expecting the frog to cooperate. Lift out waste and the surrounding fiber from the sitting spot every few days, top up with fresh damp fiber, and replace the full bed on a regular cycle before it starts to smell sour or feel compacted. Check the frog itself during those sessions: healthy skin is clean and evenly colored, while redness on the belly or legs, swelling, a frog that stops feeding entirely, or one that sits exposed on the surface instead of burying are all reasons to correct the setup promptly and consult a vet who treats amphibians if they do not resolve. Record the depth, moisture routine and full-change rhythm in his KinsLe profile, and Family Sharing means anyone who looks after him rebuilds his buried world exactly as he left it.