You use this contrast hundreds of times a day without noticing. Dogs, cars, keys and jobs all end in a z sound, not an s.
Two Languages, Same Outcome
Korean has no standalone /z/, only /s/. Spanish has a z-like sound, but it appears automatically next to certain consonants rather than existing as a category of its own. Both routes lead to the same outcome: the buzz gets dropped and everything lands on s. Because English hides this contrast at the end of enormous numbers of ordinary words, the payoff for fixing it reaches far past the pair you just tested.
Same Position, One Switched On
The tongue does exactly the same thing for both sounds, tip near the ridge behind the top teeth, narrow groove, air firing through. The difference is entirely in the throat. For z, the vocal cords vibrate at the same time, laying a low buzz under the hiss. For s, they stay silent and you get the hiss alone. If you rest a finger on your throat while switching between them, the mouth never moves and the vibration comes and goes.
The Place This Actually Matters: Plurals
Here is the part that pays off well beyond this one pair. English plural and third-person endings are written with an s, but they are frequently pronounced as z. The rule behind it is automatic: after a voiced sound, the ending turns voiced too, which is why the words in the opening line behave the way they do. So training this contrast isn't really about zoo and sue, which you will rarely confuse in context. It is about the end of a large share of English nouns and verbs, where the difference is quiet and constant and shapes how natural your speech sounds.
Where the Ending Decides the Meaning
The clearest way to hear the buzz on its own is at the end of a word, where English hides it in plain sight:
In a shop
Do you have the price?
Do you have the prize?
Both are ordinary questions and the sentence structure is identical. This is a good illustration of why the ending of a word deserves as much attention as its beginning.
More Sounds Built on That Switch
- van / fan
The same voicing switch on a different pair — worth doing back to back with this one.
- sock / shock
Stays with s and changes the shape of the air channel instead.