A common tell of someone who’s nervous while they go about a task, is fidgeting behaviour and un-focused meaningless tasking. It seems he’s trying to appear to be doing something productive, but he’s just nervously sliding boxes around and making it look like as if he’s trying to find something as he shifts about and constantly reorganizes them. If he knew he was doing a legitimate task, he’d just go about doing it, and his actions wouldn’t look so unfocused. He’d also be able to give clear and concise answers and not unintelligible mumblings or half answers. I’ve seen this behaviour a thousand times in kids when they’re caught doing something they shouldn’t be. Also, I’ve seen it in employees I’ve had working for me who I’ve caught doing things they weren’t supposed to be doing, and then suddenly tried to appear to be working diligently.