This is an excerpt from a short story/novella I'm working on. Enjoy, and tell me what you think.

David felt something squirm within his gut. It wasn’t a growl. It wasn’t a rumble. Something deep within him had shifted. Moved. Adjusted. The first few seconds after this, he sat in silence awaiting a following quiver. He waited for some sort of aftershock to prove to him he had actually felt anything in the first place. Nothing happened, and he returned to meticulously reassembling the broken pocket watch.
Minutes later, the feeling returned, not as a quiver but as an assault. It struck with such a vicious attack that David fell from his desk chair to the wooden floor tightly clutching his stomach. He whimpered in silence for a moment, the only sound being the tweezers he had slung from his hand in agony landing somewhere across the room. An echo of the pain resided in his gut like a day-old soreness. He didn’t move in fear of its return.