SRD Talk:Ooze Type
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Note that some oozes have a split ability; this provides them with a delightfully effective resistance to many an adventurer. The split ability means that an ooze takes no damage from slashing or piercing weapons, such weapons instead causing the ooze to split into two identical oozes, each with half of the original's current hit points (round down). An ooze with 10 hit points or less cannot be further split and dies if reduced to 0 hit points.
Not all oozes have this ability; examples of those that do include the Ochre Jelly and the ubiquitous Black Pudding. Silverkin 12:24, 11 May 2011 (MDT)