There's a species of squat, red, hairy creatures living in the tunnels, shambling about hungrily. The city is keeping their secret, and paying them a sizeable amount of cash. In exchange, these creatures give their pets very awkward names.
"For every good pet name, there has to be a bad one," my friend explained, "These creatures name their cats 'Sixteen Pints of Liquid Nitrogen' or 'Purple Nixon' and they name their dogs 'Ugly Feet' or 'Fffffffft Extra-Juggling' so that we don't have to. If every pet had a good name, they'd all feel average."
"But no one knows about these secret pets!" I protested.
It's a scam, I tell you. But at least my pet has a good name.