Justin Bieber's lips keep moving on CSI set

Justin Bieber proved popular with the cast and crew of CSI — despite displaying an annoying habit during scenes!

The Baby singer — who makes his acting debut on the season’s first episode — kept silently mouthing other actors’ lines!

“It’s good Justin’s got everyone’s lines memorized so he knows where he’s at in the scene, but the camera keeps catching him lip-syncing when the other actors