C.F.
Maybe he's plucking some hairs he's embarrassed to talk to you about. And why would tweezers be used in smoking pot ? OH duh.... I guess it could be used as a 'roach clip'...... but if he's passing the tests - he must Not be smoking. If you keep insisting that he's smoking - he may just do so, I would let it go for awhile. Also you'd be able to smell it on the tweezers - Have you ever Sniffed them? I'm being Serious!? Its a strong Oder and you'd pick it out right away.