I didn't solve it.
But I think mouse CAN'T cross the polygon.

If i think that mouse can go under furniture get WA3.
If can't, get WA10 at the moment.
So probably mouse can't go under furniture.

I think it can't.
I got WA3 if it can go under the furniture.
But I got AC if it can't.
Sorry,my English is very bad.