Imagine having to press down on a make-believe button when chest-pressing in the butterfly and releasing the same button to breathe. Thinking in these terms can help you better understand when to chest press and breath within the stroke cycle. Your chest presses down on the switch for the first third of the pull phase (from the point of entry to the shoulder line). After that, the chest releases the button, and the shoulders rise for the breath. To repeat the cycle, press down on the button as your arms reenter the water. Try it in practice today and see how it feels. For consistency’s sake, I recommend breathing every stroke.