Here is the passage again:
To keep the cat from sleeping on her new convertible's
canvas top. Kim leaves the garden hose out. Like a gunslinger in
a Western, she "duels" with Rocky, the family's orange tom, who hisses as
vehemently as the forceful spray of water.
The first part is an infinitive phrase fragment. It is missing a main clause, the most important component of a complete sentence.