if the edges start off jagged it does not Extrude correctly.
if the edges are tapper lets say the top of the leg thigh and you extrude down the leg then the Extrude ends up crossing edges
use zbrush DemoSoldier start at the top of the thigh leg and extrude down,
if the edges are straight it does not extrude straight, they will cross over and produce bad geometry
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