Look at the code. If frame=0 -> set the frame to 1
Without the 'Else', event 5 will then checks if frame=1, which it does, because you just set it, so it sets it back to 0 again! 'Else' is critical to make sure only the one condition is checked at a time, and you don't flip-flop your values.
What about "trigger once"? We can use trigger once for both event 4 and 5.Then it changes the frame once.