"Mums don't do that. Everybody knows that."
Mum runs the family like a well-oiled machine. She knows where every lost shoe is, who ate the last biscuit and what time everybody needs to be anywhere. She also knows exactly where the air freshener is at all times, which investigators find very convenient.
She has a perfect record. Not one conviction in fifteen years of family life. Some say it's because she's innocent. Others point out she's usually the one doing the accusing, which is a very clever place to hide.
When asked directly, Mum just smiles, says "Mums don't do that," and changes the subject to whether you've done your homework.

