"Science is dangerous; we have to keep it most carefully chained and muzzled." PAGE 225
The metaphor is effective here in describing how to deal with the burden of science. It can be both beneficial and harmful to the society. It can be implied that Mustapha Mond is comparing science to a dog. The metaphor provides an example that readers can relate to. Apparently the society is based on a sort of science of its own. There must be the perfect balance between several aspects to make everything work. When the people themselves do not conform or differ in thought, they try to do the same thing with them. If they are not quiet about their ideas, they send them away to prevent them from corrupting the whole society. It seems a little harsh, but they are worried about the stability of the society as a whole. Even the controller knows what it is like to be threatened to be sent away, but he is about to send away Helmholtz, Bernard, and John.