What exactly does that mean, "onion breath" about a dog?
Hi, I have a question about "onion breath" about a dog.
Three Ameicans (Native speakers) mentioned "onion breath?" in the course of conversation when I talked about my dog who looked for the crumbs someone dropped on the ground at the cafe and he found a onion.
why did they ever come up with that "onion breath"?
Your answer is very much appreciated.My dog hasn't bad breath problem though.

Question

What exactly does that mean, "onion breath" about a dog?
Hi, I have a question about "onion breath" about a dog.
Three Ameicans (Native speakers) mentioned "onion breath?" in the course of conversation when I talked about my dog who looked for the crumbs someone dropped on the ground at the cafe and he found a onion.
why did they ever come up with that "onion breath"? 
Your answer is very much appreciated.My dog hasn't bad breath problem though.

Answer

Have you ever smelled someone's breath after they ate a lot of onions?  It has a specific smell, so we call that smell "onion breath."  If your dog ate some onions, it could have "onion breath".

It also sounds a little nicer than just "bad breath" which could be many different smells.

Answer

Ha ha, dogs are the only one that can have onion breath. People can have it after a meal. Another term I like to use is dragon breath. It's similar: bad breath, but not necessarily attributed to onions. Someone might wake up with dragon breath.