How to kick in Butterfly. In Butterfly, the kick is also known as the dolphin kick. The kick is like a wave-like motion. You want to kick from your hips, with the slight bend in your knees. Your heels should just come out of the water when you do the Butterfly. You don't want to have too much splashing, with all of your feet coming out of the water, or have your feet to be too low, sinking to the bottom.
The feet should be right on the surface of the water, in a wave-like motion; doing it in a relaxed way, where your ankles are floppy and your toes are pointed, and your knees are slightly bent, and both legs are kicking at the same time, like a dolphin. When doing the Butterfly, there are typically two kicks per stroke. The first kick is in the beginning of the pool, and the second kick is at the end, to help your arms recover. All of that works in rhythm to have a perfect Butterfly. That's how we kick in Butterfly.