I stumbled on this, from a story from a dozen years ago: As animals get bigger, from tiny shrew to huge blue whale, pulse rates slow down and life spans stretch out longer, conspiring so that the number of heartbeats during an average stay on Earth tends to be roughly the same, around a billion. A mouse just uses them up more quickly than an elephant. If that doesn't beat all. I'm going to look around for more references to this incredible idea -- that all animals get about a billion ...