This brown-and-yellow sludge appears to be made of multiple smaller globules churning in a disgusting communal mass.
Str 4, Dex 16, Con —, Int 3, Wis 9, Cha 11
A target that takes swarm damage from an undigested swarm is covered in acidic slime and must succeed at a DC 16 Reflex save or take 2d6 points of acid damage for 1d4 rounds at the start of its turn. An affected creature can make a new save as a full-round action.
Organization solitary, pack (2–5), or infestation (6–12)
Washing off the acid grants a +4 bonus on this save. The save DC is Constitution-based.
Whereas individual undigested are more of a nuisance than a threat to adventurers, a swarm of such creatures can be dangerous to even experienced adventurers.
An undigested swarm comprises hundreds of individual undigested. Driven by insatiable hunger, they fall upon and consume any living creatures crossing their path, surrounding the unfortunate victims and drenching them in acidic slime, digesting their still-living prey even before the screaming ends.
Pathfinder Roleplaying Game Bestiary 5 © 2015, Paizo Inc.; Authors: Dennis Baker, Jesse Benner, John Bennett, Logan Bonner, Creighton Broadhurst, Robert Brookes, Benjamin Bruck, Jason Bulmahn, Adam Daigle, Thurston Hillman, Eric Hindley, Joe Homes, James Jacobs, Amanda Hamon Kunz, Ben McFarland, Jason Nelson, Thom Phillips, Stephen Radney-MacFarland, Alistair Rigg, Alex Riggs, David N. Ross, Wes Schneider, David Schwartz, Mark Seifter, Mike Shel, James L. Sutter, and Linda Zayas-Palmer.