Revealing mistake: Prue is needed in the storm drain to rescue Piper, who is stuck in a hole bottomed off by a metal circular guard. Prue uses her power to levitate the metal circle to her level. When the camera pans out, the metal rods used to actually levitate the metal circle are visible. (00:36:25)
Continuity mistake: After the Grimlock kidnaps the child getting the ball, Prue goes after it. But the demon opens a hole in the earth and jumps through it and it closes. Prue then reaches the spot where the Grimlock disappeared and she is surrounded by dead leaves and trees. Then it goes to another shot of Prue turning around. Suddenly the trees and dead leaves are gone and she is standing in an open area with green grass and no trees.
Answer: "Hush, Hush, Hush" Paula Cole.