Lapse

I spent this morning teaching the anatomy of the female breast to medical students. We teach them in small groups that rotate from teacher to teacher, so I repeated my “lesson” 4 times.
Why then, in 2 of those sessions did the word “intercostal” vanish from my brain? No, I wasn’t distracted.
It’s a perfectly normal and common anatomical term (meaning “between the ribs”). I used it in 2 sessions quite happily. So where did it go for the other 2? As hard as I might try, I just couldn’t recall it. Oh well. I leave the neuroscience to Prof. O’Brien.