It was at a working ranch in southern California. The riding horses are all Geldings. My second time out, I was riding a mottled grey named "Concho". As we were departing the stables and heading to the trail, Concho would occasionally bend his neck to the side and (it seemed to me) would be looking at me on his back. After repeating this a few times, he would follow up by letting out a deep whinny. He whinnied repeatedly with intervals of rest ranging from 15 seconds to 2 minutes. This behavior was limited to when we were leaving and returning to the corral, and was sometimes answered by whinnies from the horses in the corral (not the horses in our group).
My girlfriend's mother had never seen such repeated whinnying in a horse and she has been coming to the ranch for half a century and riding like it was her job. The wrangler leading us also found the behavior to be highly uncharacteristic.
Anyhow, the experience really got me wondering what was causing it. I rode Concho a second time the next day and he did the same thing. He doesn't behave this way with other riders.
Anyone have any ideas what that horse was thinking?