It is understood that the nostril of the horse is what creates the illusion of grandeur….
If a human climbs on the back of a water horse, the horse will often dive into the water and drown its rider. If a human gains control over the horse it can be put to work in fields….
Water Horses have the strength of ten land horses and do not like to be enslaved and will try every trick to escape. The water horse then courts its master for several years before it consumes only the left leg and right hand pinky finger of the victim.
"Kelpie - Wikipedia (the kelpie is a supernatural water horse from Celtic folklore)
So now the real question is, why did the Celtic people value the left leg and right pinky finger above other appendages?
Moral of the story: beware the nostril