You have reassembled the malfunctioning item all bar the final screw (1x2mm) the law of chaos then kicks in
You need the loo,the lioness starts vacuuming as soon as you have left the room,your son "tidies up"for the first time since the onset of puberty.By the time you come back the screw has gone "no one has touched it" the tray you were working on and the job have been put away.The mysterious son has disappeared.
First the dust bag,opened out outside(it is always cold)a finger tip and magnetic search is conducted nothing ,the contents are now blowing about and need cleaning up (the lioness is watching the mess and pursing her lips) the mysterious son appears slips his arm around his mother they both laugh.
The job is fetched and shown to me through the glass,there taped neatly to it with clear sellotape is a tiny screw Doh!!