The back story...
A naturalist/guide was clearing a trail through a patch of virgin rainforest when the fangs penetrated his shirt. The viper's teeth sunk into his arm and inoculated the victim with a potent toxin. We were listening acutely to the story as Michael Sevilla led us across the suspension bridge and into the jungle. Call it a coincidence, but a hognosed pit-viper (Porthidium nasutum) now sits in a tight coil blocking our path through the forest. Michael, our photo-guide and naturalist, explained that his friend is in a hospital bed unsure of his fate. It took a while to transport the victim to the nearest emergency facility, and discussions about necrotic tissue and possible amputation ensued. Our viper is unfazed by our presence, and is unwilling to move. It's a small animal... less than a meter long, unglamorous, and well camouflaged. The reddish-brown color is broken by dark splotches that make this serpent cryptic in the understory of the forest. Unperturbed by our presence, the viper sat poised, coiled, and prepared to strike. Eventually, the extended leg of a tripod and repeated agitations had the desired affect. Unenthused by the relentless prodding, the snake slithered off the trail and into the leaf litter.
To produce this image I attached a Canon 180mm L-macro lens to my 5D Mark II and positioned the tripod in the same plane as the snake. The 180mm macro allows me to produce life-size images while maintaining a not threatening working distance. With the lens aperture set to f/4.5, there was enough depth of field to maintain sharpness across the head of the viper, while allowing the background to fall out of focus.
Final note... during our last day at Selva Verde, we learned that Michael's friend has recovered from his altercation with the viper... no doubt he may a bit wary when it comes to snakes, be has survived and will likely be out hiking a forest trail in no time.