How should I record my business transactions? Purchases, sales, payroll, and other transactions you have in your business generate supporting documents. These documents contain information you need to record in your books. What is the burden of proof? The responsibility to substantiate entries, deductions, and statements made on your tax returns is known as the burden of proof.
Mice will probably open their eyes when they're about 10-14 days  old. About the time the hair is fully covering them they open their  eyes.
That's why they are born with their eyes closed. A kitten's eyes will continue to develop after birth for about a week, at which point you'll notice that her eyes start to open very slowly. It can take up to three weeks before a kitten's eyes are entirely open.