Changing on the fly...
One of the most important and unique aspects of the game of hockey. Do it right and you never even notice that it happened, but do it wrong and... well... Predators fans are intimately familiar with the atrocities of bad line changes. (You knew what that link was before you even clicked it, didn't you?)
It's important to pick your moment to change on the fly carefully so that you don't leave your teammates unsupported. The first and third periods are easy enough to change on the fly as your bench is in your defensive zone, but during the second period?