Beginning in NetHack 3.6.0, the black pudding, brown pudding, gray ooze and green slime drop a glob instead of a corpse. Globs differ from corpses in that like types of globs merge into larger globs with greater nutrition, and globs cannot be sacrificed. Globs were added to make pudding farming less effective.
Globs do become tainted and cause food poisoning, just as corpses do, but will never fully rot away.
In NetHack 3.6.0, globs could not give resistances when eaten. This was fixed in 3.6.1.
Since most variants are based on NetHack 3.4.3, they do not have globs. Monsters that leave globs in vanilla leave corpses instead.