Grocer's apostrophe

Errors, typos and general idiocy on this blog aside,  I generally notice grammatical and typographical howlers. I don't go looking for them: they throw themselves at me. I can't ignore them, because to me they are as obvious as a fox in a hen coop. They distract me, and if a book or article I am reading is full of misplaced apostrophes, or misused semi-colons it spoils my enjoyment of it.

The fan has a similar ability with music. He'll listen to me play a piece - even a piece he doesn't know - and he'll tell me that the timing must be wrong, because he can hear that I'm not playing a full bar somewhere, or I've got an extra beat. Recently he listened to me playing Horsburgh Castle and said I was playing an extra phrase somewhere. I was adamant that I was not, that I was following the dots, that all was well. We listened to Seudan play it. Sounded good to me, the fan was not convinced.

I went back to the dots, he listened, pinpointed the offending two notes, I looked at the dots *again*...and sure enough, he was quite right. In the B part I've been playing the first bar of the first ending at the start of the second ending. It really does amount to two notes. I'm still not sure that I can hear the difference, but the fan is happier. I'm not sure how you learn to hear the musical equivalent of the grocer's apostrophe, but I clearly need to.

It's harder by far to pick up errors in your own writing, I think because you are focussed on content and what you *think* you've written, because writing is only expressing visually that which is already in your head. I don't know if this pertains to music, too.