The feathers/fur/sparks will fly informal
Used to mean that an argument or a fight is going to happen.
If you talk back to her opinion, the furs will fly.
When they came across each other, I knew that the sparks would fly.
The politician has delivered a controversial speech. They bet that the feathers will fly.
This term was first used in the United States in the early 19th century. The image depicts a ferocious dog or cat battle.
Meaning absolutely certain or without a doubt
I am as sure as God made little green apples that Peter's the one for you, you two make a beautiful couple.