Oxybelis aeneus  Brown Vine Snakel
This specimen is not acting in an agressive manner.  Instead brown vine snake opens their mouths when they are frightened.  These slender snakes are active during the day and are not uncommon in the scrub vegetation in and near Mocoron as well as the  pine savannahs of Gracias a Dios.i..ck here to add your text.