all+the+dogs+let+out+blood-curdling+growls+and+showed+their+side+teeth

The words of Napoleon (representing Stalin) were so powerful. Every animals followed and obeyed Napoleon when he said or ordered something. In this passage, or sentence, all the dogs growled, because Napoleon became furious, of the Snowball's return.

It also goes deeper than this. The power and interference of the military. LP

This is what Napoleon has done to the animals in Animal Farm. He has done a very good job of brainwashing the animals into thinking Snowball is evil through the use of Propaganda and false rumors. The dogs showing this much anger just by the mentioning by Snowball's name tells us that similar reactions may occur in other animals and also that Napoleon is a very good "leader".