As an exercise, let's rephrase this sentence favoring each of the senses in turn:
SOUND: "The alien spider crunches John's ankle in its gnashing, clicking jaws and John screams and screams."
SIGHT: "The alien spider drags its glinting needled jaws across John's pale ankle, gouging wet red lacerations like a fork through butter"
TOUCH: "The alien spider's cold needle jaws smoothly puncture John's ankle and stinging pain explodes up his leg like rolling napalm."
SMELL: "John's head swims in a cloud of sweat and fear and the stench of decay spilling from the alien spider's wide, ratcheting mouth, then those needle jaws snap shut and the air turns to copper."
TASTE: "The alien spider chomps hungrily on John's ankle and John shrieks through gritted teeth, biting his lip and flooding his mouth with warm, salty blood."
Writing isn't just putting one word in front of another. It's about knowing what you want the reader to see and feel at this point in the story and about building sentences that make your reader experience the story your way.
* I'm reading David Wong's
This Book is Full of Spiders which may or may not have influenced this post but certainly did.