The bushes rustled in the wind, but he didn't move a muscle. His gaze never waved from the spot in the tall grass. For hours nothing came out of the hole, but he didn't falter, secure in his conviction that his perseverance would be rewarded.
Finally, movement. In a heartbeat he sprung up out of his crouch and catapulted himself across the garden.
His jaw closed across the frail neck with a snap, instantly ending the mouse's life. He threw his head back and proudly pranced back towards the house, anxious to show off the spoils of his hunt.
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Solid tone, fun personification. Details like "the bushes rustled in the wind" work, and I have a love affair with action verbs, so "catapulted" is delicious (and a nice play on words).
Nitpicky:
"In a heartbeat" is cliche. Another way to say it?
"Instantly" is implied by the action, I think, that it becomes repetitive.
Watch your pronoun-subject agreements. Sometimes "he" is referring to something besides the cat, based on what "he" follows, subject-wise.