Of all the things that can go wrong with a clarinet, this tale is about perhaps one of the most unusual I've ever seen.

My client, the very highly talented Dunstan Coulber, called in just after the Christmas festivities with an intermittent problem on his clarinet. It seems the instrument was functioning perfectly up until New Year's Eve, when, in the middle of a gig, it just stopped playing.
An impromptu and no doubt slightly desperate examination revealed no cause - and even more frustratingly the clarinet was found to be working again some moments later...only to fail again shortly afterwards.
This is obviously a very worrying prospect for a professional player, so at the earliest opportunity the instrument was whipped down to the workshop for an examination.

In general terms, the more widespread the symptoms the higher up the instrument the problem is likely to be found - so straightaway I focussed my attention on the top joint. A quick blow test revealed no leaks, so I suspected some kind of mechanical problem.

There are a number of problems that can result in intermittent faults, the most common being a loose pad. If a pad comes adrift it tends to make itself known by promptly falling off the instrument, accompanied by a sigh or a ribald cheer, depending on which end of the instrument you are - but on the top joint of a clarinet the pads sometimes don't have enough clearance to fall completely out when the keys are operated.
All that happens is that the pad rotates in the cup, sometimes coming down to seal the hole, sometimes not.

I couldn't find any loose pads, so my next suspect was a sticking flat spring.
Where the tip of the spring contacts the body there's usually small metal plate, put there to prevent the spring tip from gouging a hole in the body of the instrument. Sometimes burrs can form on this plate, preventing the spring from fully travelling back when the key is closed.
This has the effect of holding the key fractionally open sometimes.
I then found that the second trill key had a slight 'blip' in its action. Just before the key closed there was a slight hesitation - exactly the sort of symptom you'd expect with a burr on the spring plate...though it could also indicate a slightly bent key, causing it to rub up against adjacent keys.
I couldn't see any touching keywork, so I put my money on the spring plate as being the culprit.

I duly removed the trill keys and refitted the second key to check the action - but now it ran quite smoothly, and no amount of manipulating the spring would duplicate the hesitation I'd found. I was about admit that I was perplexed when I noticed something that ought not to have been there. It was a small, cylindrical, shiny bead - of the sort you find in those 'make your own necklace' kits.
Nothing special about that in itself - assorted debris often finds its way into the action of an instrument, but usually drops off as soon as the horn is moved or lifted up. But this little bead had found the most perfect spot in which to lodge and wreak havoc.

Each trill key has a flat spring fitted to it, and this spring is held in place by a small screw.
On some clarinets there's a corresponding hole in the body underneath the screw head to prevent the head touching the body and thus preventing the key from closing fully. Our little bead had found itself a cosy home in one of these holes - and such was its size and shape that once it had fallen into the hole it was unable to fall back out unless the clarinet was inverted, the corresponding key opened fully and the whole thing given a bit of a shake.
Not exactly the first course of action that springs to mind when you're on a gig and the band's racing towards your next chorus.

So there the bead sat, and from time to time it worked its way round to exactly the right position to butt up against the head of the spring screw as the key closed, thus just preventing the pad from fully closing and stopping the whole clarinet dead in its tracks.

Dunstan then informed me that his girlfriend makes jewellery - so that was how the bead came to be there in the first place.
It comes to something when problem solving has to be extended to asking the client what his or her partner gets up to on the sly. I foresee much merrymaking amongst the clarinet sections of assorted orchestras as various players try to sabotage each other's clarinets with a proliferation of sneaky beading.