I think that corruption happens when someone doesn't stay true to their gem.

Centipeedle- I said that the Centipeedle is Emerald because of Emerald is the stone of vision. Actual Emerald is supposed to protect love and to cause security in love between a couple. The Centipeedle shrieks every time it sees Garnet's knuckles. When the knuckles shine it screams and gets defensive. It's scared of Sapphire. Ruby has gloves so it can't be her. My theory is that instead of staying true to her gem she grew jealous of Ruby and Sapphire. Hence the green eyed monster, that we call the Centipeedle. She tries to split them up instead of bringing them closer so her gem took control and pushed her into the deepest depths of the gem. Her gem now is in control and not her.

This is supported by Amethyst.

Amethyst- a stone of calming energy and reduces overindulgence. When Amethyst poofed her gem was trying to take control. That's when she knew she had to change. She came back as herself and her personality was a little different. In "cry for help." We see that she has in fact matured. She's gotten a lot calmer and she doesn't eat like crazy anymore. She also doesn't sleep as much as she did. Her poofing was a wake up call to her that she needed to change or her gem will take over.