In a word, "brutally." In examining what Napoleon does to the hens as well as the other animals that might have displayed disloyalty, it is a brutal moment. It is also an instant where it becomes clear to the reader, and most of the animals, that what Napoleon is as a leader is something that is both horrifying and something unstoppable. The assembling of the animals together in chapter 7 is first done to acknowledge Napoleon's own greatness. In this hue of self- glorification, any animal that had been involved with Snowball or had openly declared opposition or dissent to Napoleon have their throats ripped out by the pack of Napoleon's guard dogs. More animals who confess are destroyed by the dogs. This bloodshed is savage to even witness, something that confuses Clover into seeing that what is unfolding cannot be the original intent of Animalism, Old Major's speech, and certainly the commandments. In the end, this becomes the penultimate statement as to how those who speak out against Napoleon will be addressed. Power and authority are shown to be absolute with Napoleon, a fact that is only confirmed through his unspeakable brutality and savage cruelty.
The Hens had their throats ripped out by the dogs of Napoleon.