Toyota shop noted cat and bird food in the air cleaner of our 2008 Prius( we recognized it). They replaced the filter and screened some openings. A few days later we began smelling what could only be dead rodent smell coming from dashboard vents - awful! They looked at everywhere they could but found nothing. To do a complete check will require removing the instrument panel, etc. at great expense. They said keep the windows open and it will eventually go away. I said no way, we can’t drive it that way. Our insurance adjuster says it will be covered by comprehensive if they find a dead rodent. If not, it is our problem. Our son suggests keeping a ripe, dead rodent on hand. What is your suggestion? (From what I can see online, Prius can be described as a mouse hotel!)
You have no choice unless someone can find something with a boroscope or mini camera.