Original: She passes over a skunk, a siamese cat, and a cat with an eye infection before finally deciding upon Snowball III. He drowns trying to catch a goldfish in an aquarium while Lisa is preparing his cat food in the kitchen for the first time.
Simplified: The third version of Snowball was a male cat named Snowball III and was killed when he drowned after he tried to catch a goldfish in the aquarium while Lisa was in the kitchen preparing his cat food for the first time.