You vs 1000 rats
Obviously one rat is no threat to a human, but in numbers they could become a deadly menace.
Here are the rules:
You are alone and unarmed. You're dressed in a t-shirt and jeans. You're ready for the rats and know they're coming, and the rats are going in for the kill. You're in a house without furniture or doors to the rooms, but there is an upstairs you can access.
How many rats do you think you can defeat at one time? How many would it take to overwhelm you?
For argument's sake, the rats don't have any disease they can communicate to you.