The EMMI kill in different ways.
Getting used to the timing for the EMMI's one-shot blow can seem impossible to survive. Even with two extra-thin windows for countering their attack, you're still likely to die when caught. What's worse is that each EMMI has a unique timing for their attacks, and they can switch how they kill Samus. Instead of trying to learn the timings, do what ADAM says, and avoid them at all costs.