If this should ever happen to you, do not pull the nail or any foreign object which could get lodged into a hoof, without having radiographs first.
We recently did quite a bit of construction on our barn, and working with the builders I continued to stress the importance of making sure no nails were left on the ground, and this is the reason why.
I recall the story years ago of a lovely dressage horse who did not survive a similar incident. The farm owner who was not directly responsible, was liable because the horse was legally under his "Care, Custody and Control". Had he not had insurance coverage for this, he would have personally been responsible for damages.
This just happened to a good friend who recently had some fencing done. In spite of the care the builders took and effort she made, one lone nail can do this. An endurance rider who just completed a 50 mile event in good form now has her program sidelined.
She has been all night, soaking, medicating and worrying. No matter how careful everone was this happened. Still as in this case just one nail that falls from the tool belt, and then gets swallowed up by leaves can be devastating.
So be vigilant and make sure your contractors and all who work for them are careful.
It’s another version of Murphy’s law. In spite of all that was done to clean up a work site, the one nail no one could find found the hoof of this horse.