This is the last standing still lesson!
I suggest, to wrap this up, that you do not leave your horse with a bridle on and walk away until you are absolutely positive he will not walk away and step through his reins. Again, use your own judgement for this! Just be aware that this could hurt him badly and may wreck your bridle. Even the horse that is the most reliably trained will spook or jump occasionally – they are herd animals, and prey animals, too, and this is simply built into their nature. There is nothing you can do about it!