How was Snowball used by Napoleon to his advantage?

Snowball was used to frighten the other animals and keep them submissive.

A rumor begins circulating among the animals that Snowball is sneaking into the farm at night and causing mischief. From then on, the animals attribute any misfortune to Snowball’s interference. Napoleon arranges a public investigation of Snowball’s activities. He surveys the farm and claims to smell Snowball’s scent everywhere. The animals are terrified. That evening, Squealer tells the animals that Snowball now belongs to Mr. Frederick, with whom he is plotting to overtake Animal Farm. He claims that Snowball was collaborating with Mr. Jones from the very beginning and claims to have supporting evidence. Squealer also claims that Snowball intended to get the animals killed in the Battle of the Cowshed. When the animals, including Boxer, protest, Squealer invents yet another lie. He claims that Napoleon cried, “Death to Humanity!” during the battle and bit Mr. Jones in the leg. Boxer continues to protest until Squealer tells him that the news is directly from Napoleon. Boxer replies, “If Comrade Napoleon says it, it must be right” (91). Before leaving, Squealer gives Boxer a nasty look and warns the animals that Snowball’s secret agents are lurking among them.