Could a mouse kill a bear?

I’m planning for a Mouse Guard game that will culminate in the players facing down a bear!

The rules cover such scenarios far too briefly, only stating that you would need 20,000 mice to do so (via the War skill). This seems like far too few mice to wage war on a bear, also how would this even be done? Are the mice laying siege to the bear, or are they marching on it? Do you even use War? Could a single mouse climb the bear, insert itself into the ear, and assassinate the bear?

I realise that this is a task for the players to decide on but I want to prepare for the circumstances.

How do you kill a bear with mice? (and how can I prepare for this?)