Say cat, then make it plural: cats. Many learners either add a vowel ("cat-ess") or drop a sound ("cat" or "cass"). Native speakers do something else: they fuse the T and the S into a single tight sound, /ts/, the same buzz-free "ts" you hear in pizza.
Its voiced partner is /dz/, as in kids and needs. Master these two blends and your plurals, verbs, and contractions instantly sound cleaner.
The Rule
When a word ends in T and you add the -s ending, the two combine into /ts/ (one motion, no vowel): cats, hats, lights, sits, waits, it's, that's, gets. When a word ends in D, they combine into /dz/, the voiced version: kids, needs, beds, reads, roads, ends, words. The key is to keep your tongue on the ridge behind your teeth for the T or D, then release directly into the S/Z hiss without moving away. No extra vowel goes between them.
Practice Words
When There Is No Blend
The blend only forms when T or D sits right before the ending. If a vowel already separates them, you get a full extra syllable instead: after the sounds /t/ and /d/ that follow another vowel plus -es, words like dates stay /ts/, but cities, ladies, and waited add a clear /ɪ/ and do not blend. Also, endings like -ths (months, fifths) are a different, harder cluster. Focus the /ts/ and /dz/ rule on plain T+S and D+Z at the end of a word.
Quick Tip
Practice with the German or Italian "z": the ts in pizza is exactly the end of cats. Buzz your voice on for /dz/ and you have the end of kids. Say them back to back: cats-kids, hats-heads, lights-rides.