I could tell that he'd been focussing obsessively on the rhythm and tempo of a particular section. It had a FIVE-tuplet, and a SIX-tuplet as well. First Tuplets of his life - this was worth obsessing over. Unfortunately, he was now in that weird short-circuity brain place where he couldn't put all of the notes in the pattern at the speed that was the only speed he knew to go, and the more we tried to slow it down the goofier his fingers got, because all he could think about was the transition from 4 to 5 and from 5 to 6 that he'd been working on.
So we used my favorite trick. Play it slowly, I said - so slowly that you cannot make a mistake. I don't care about the rhythm, I don't care about the tempo - just one note after another, as slowly as necessary with NO mistakes.
He did. Sometimes he had to sit on a single note for more than a full second, thinking about the next one - but he got through the passage, note by note, with every one correct.
Do it again, I said. Don't even think about the rhythm, and if you are ready you can allow yourself to play faster, but go as slowly as necessary to play every note right.
Do it again, I said. Let the music ease toward the rhythm you know, but stay as slow as you have to, because I want all of the notes to be beautiful.
We went around several times. I was not interested in putting him back in the stress place from which he could not (but thought he could) play.
He played so beautifully. By the end of a few minutes, the rhythm was approximate and the tempo was close - we weren't performance ready, in other words, but we had created a version of those few measures that he could be proud of, and build on, and grow from, and finesse later up to speed.
I had forgotten how much I love slow practice. Not the deadly turn-your-metronome-on and keep-grinding-through-until-your-lips-melt kind of slow practice, although that has its (very occasional) place - but just this game of Let's Play Beautifully. Let's Take Care of Business. Let's be gentle with ourselves and not make the music go fast until it's ready to. And, in my case, Let's just see how much of this is actually memorized and how much of it is just habit and if I get stuck, can I think my way out?
Update: Mendelssohn memorization is progressing. Slowly.