Which of the following sentences does not use a semicolon correctly?

O Cows are social animals, and they don't like to be alone.

O Cows don't actually have four stomachs; they have one stomach with four compartments.

O Cows form meaningful friendships and often have best friends; these friendships make them happier, calmer, and actually smarter.

O Cows have an excellent sense of smell; they'll come running if they smell alfalfa cubes, their favorite snack.