Coriander — Food safety facts
Safe to share · Cats · full breakdown on the linked food page
Safe in small amounts, both the seed and the leaf.
The full verdict, portion guidance and serving notes are collected on the Coriander food facts page.
Short answer
Coriander is safe for cats, so a little sniffing isn't a health risk. It's still a good habit to teach 'leave it' for any houseplants, to prevent chewing on ones that might be toxic. Offer your cat some cat grass instead, and call your own vet if you ever notice vomiting or unusual behavior.