Animals reproduce by fertilization, where an egg cell combines with a sperm cell to start the development of a new individual. Most animals only allow one sperm to enter the egg to prevent problems. To control this, animals have a quick electrical block on the egg's surface that stops extra sperm from entering. This block is tied to a rise in calcium levels inside the egg. Amphibians are studied to understand how this process works in vertebrates. Scientists have looked at how this electrical block to stop multiple sperms is similar and different in various animals, showing it's a typical yet diverse process across different species. The connection between the quick electrical block and calcium increase inside egg cells is crucial for the evolution of fertilization methods in animals.