Zoe Q and E Look and Sound Too Much Alike
It is easy to confuse one for the other while they are travelling: Zoe's E should be as distinct as other highly impactful spells. Specifically, both abilities are announced by a soft popping sound and appear as pale projectiles. Zoe's E is an AOE slow, two second stun, and damage amp. This ability is highly impactful: it can set a squishy up to be chunked out or stop a diver in his tracks. Zoe's Q, on the other hand, is a poke spell that might be willingly tanked by a diver, tank, or other champion who needs to close the gap. As long as both spells sound and look alike, players will either confuse E for a Q and be locked down, confuse Q for E and be chunked in early laning, or have to spend precious moments figuring out which one is coming, missing opportunities for kills or getting attacked by teammates. This is not fun because it reduces the chance for counterplay.
If, on the other hand, Zoe's E sounded and looked very different from her Q, then players could distinguish her abilities and respond accordingly. Hear an E from across a wall where you saw Zoe a second ago? Get ready to dodge or flash. See a Q while laning? Walk behind your minions. With this chance for counterplay, laning and teamfighting against Zoe could be fun instead.