So it is, the rise is organized and methodic when at all possible. The most notable exception is when there is a surprise. Same thing sometimes happens with a fish when a fly smacks down right on his nose. Since the preferred rise and take angle remains constant whenever possible, it can be assumed there is a reason. We shall investigate that reason in relation to other factors as we progress.
Light does things with angles too.
As it enters water it bends. Light will bend when it leaves or enters any medium which is either thicker or thinner than the one from which it emanated. Any kid knows this when poking a stick into a stream at something. It is not where it looks like. Where you see it, is not really where it is.