Well, fifty words is less than 100 so I guess you didn't miss it.
The length of the first sentence does, imho, a bad job at showing the stakes for the main character; maybe you should split it in two sentences and thus change the reader focus to the sneaky bastard. "The snake silently slithered behind it,... " .
Also "dehydration" sound better than "lack of water".Plus, you'd have gained some extra words. I think "falter" would be a better description for the chicken action instead of simply stopping. That kind of things would flesh out a bit the story. "The characters never say things, they state, declare, stutter, mumble, etc." . Same thing here.
"A hawk shrieked and the snake was no more" could be, I guess, better than simply stating "flew from the sky". "Fell from the sky", at least, is not a pleonasm. Pleonasms are bad. Especially when you have to pick your words carefully.
btw, the snakes that are in the desert are really small,aren't they? eating small rodents and all? And I'll assume the chicken fell from a caravan or something because idk why they would go where there food is scarce.
Well I'm not sure my feedbacks are helpful, but here's my two cents.
ps: took me way too long to write this