Exactly the same mouth as /s/. Voice ON — zzzzz, like a bee.
Check yourself: Hand on your throat: /z/ buzzes, /s/ does not. Same tongue for both.
Watch for: /s/.
◆ marks a word that does NOT follow today's pattern — Blumenfeld boxes these on the page. Teach it by heart; do not let the class sound it out and lose faith in the rule.
Say the word, have them repeat it, count the sounds on fingers, THEN write. The count is what stops a child writing the first letter and guessing the rest.