the fur will fly
the fur flies
There is an argument. When the fur flies, I'm making myself scarce—there's no way I'm getting roped into a fight between those two. You can be sure that the fur will fly if the president vetoes the bill that both sides of congress worked so hard to pass.
the fur will flythere will be serious, perhaps violent, trouble. informal
This phrase originated in the early 19th century, in the US. The image is of a furious fight between dogs or cats.