Animal Farm: What confession come from the four pigs who were attacked by Napoleon's dogs?

From the text:

They were the same four pigs as had protested when Napoleon abolished the Sunday Meetings. Without any further prompting they confessed that they had been secretly in touch with Snowball ever since his expulsion, that they had collaborated with him in destroying the windmill, and that they had entered into an agreement with him to hand over Animal Farm to Mr. Frederick. They added that Snowball had privately admitted to them that he had been Jones's secret agent for years past. When they had finished their confession, the dogs promptly tore their throats out