Strange piece of plastic inside my iPhone 4

Hello guys! I've noticed a tiny piece of plastic inside my iPhone 4. I've tried to remove it from the phone but I can't do it. Is like its hooked inside it. The phone is just three months old and has been always used with an Apple bumper. I don't know if it was there when I bought it, that would mean it's a manufacturing defect, but I don't think it was. What do you think it is? Here you have some pics taken with another iPhone.

https://www.dropbox.com/sh/1r5nc3by4x9tiug/AvY3f9RPO1