Would a 185 lbs man that's been thrown from a horse be able to make a dent in a harmonica?
Annie Proulx's Jack Twist more than likely weighed no more than 150 lbs and maybe not even 140. Her Jack was rather short and his big haunch, larger than normal thighs and hips, were not exactly fat. There are many professional bull riders built just like Jack's description in the book. More than likely the flattened harmonica had been in Jack's shirt pocket when he fell off the horse. Or, he could have been playing it when the skittish bay mare threw him off. The ol' gal might have been a music critic.