Prey, upon viewing a predator, often call attention to themselves, by making noise, by jumping about, or in other ways. The traditional explanation is that they are informing their own group that a predator is nearby. Animals are sometimes encumbered by huge features, a peacock's tail, the extinct Irish Elk's 20-foot wide antlers. The traditional explanations are varied, perhaps heredity gone haywire. Some prey are brightly colored, perhaps they are actually camouflaged under some circumstances.
Altruism is often a mystery, with one animal sacrificing itself for others.
Traditionally, altruism makes sense only when it saves one's own offspring. The Handicap Principle shows that animals handicap themselves to show their fitness. A prey animal calls attention to itself to show the predator that he needn't bother chasing this fine specimen, because it won't work. Huge features show the females that this guy is very fit, and is worthy of mating. This book is apparently very important to biology, clearing up some persistent mysteries.