I was coming back from lunch one day when I met a coworker frantically coming down the path towards me. The news, to put it lightly, wasn't the best - a cobra had escaped. No, the crisis was already over - it had been found and recaptured. Sort of. Actually, it been recaptured then found... Another keeper in another department had found the snake slinking about. She'd thought it had been a wild snake, albeit of a species that she'd never seen before. She brought it to the Reptile Curator. That's how we all found out that the cobra had been loose.
That was about ten years and three zoos ago for me. Yet every time I remember that incident, my stomach drops to my feet.
If I had to name the ultimate escape artists of the zoo, I'd have to call it a tie. On one hand you have the monkeys - so fast, so agile, and so quick to notice when you aren't paying attention or if you've made a mistake. On the other are the snakes - quiet, fluid, and incredibly capable of disappearing through the tiniest of holes. Whereas an escaped monkey tends to run around and create a commotion, however, a snake slithers out of sight and, for all practical purposes, vanishes.
Looking at all of the zoo memoirs I have, I'm amazed at how many of them prominently feature escape snakes and the pursuit thereof. Sailing with Noah. Man in a Cage. Probably the most exciting chapter of You Belong In A Zoo! details the search for an escaped king cobra in the Bronx Zoo's World of Reptiles, a hunt which stretched out for several days.
For as little as they really seem to move, snakes are incredibly adept at escaping. They are extraordinary flexible and can fit into surprisingly small holes (which, it turns out, is how our wayward cobra got out). They also tend to be excellent climbers. Their natural history consists largely of exploring and probing tunnels and cavities for prey, so they are naturally inclined to look for crevices to slip through. For as much as people say about how unintelligent reptiles are, I've also found them to be fairly curious, and they will readily investigate their enclosures.
Even more of a nightmare, however, is what happens once they get out. Snakes don't move too much, so once they've found a new hiding space, they're apt to stay there. Nor do they eat much, so good luck luring them out for food. They're silent, so good luck hearing them. And again, they can find the smallest nooks and crannies to hide in. The king cobra that Brazaitis sought was eventually found lurking in the ceiling of the reptile house... directly above the crocodile pool.
I distinctly remember one young python which vanished at a zoo where I worked. It had been housed in a tank in an off-exhibit holding area, along with several other reptiles. We found it... but not before x-raying every single monitor lizard and crocodilian in that holding area to make sure none of them had found it first and eaten it.
I've heard of a lot of methods used to recapture an elusive snake. Sprinkle flour or other powder on the floor so you can see if they slithered by when you aren't around. Put up little hide boxes for them, check later to see if they've moved in. Turn the temperature down, then put up a heat lamp for them in a prominent place. Ultimately, it comes down to a lot of patience and even more luck.