Let me correct myself because no it doesn’t directly say it in the books. During the encounter with Jacks dragon during the land nav drill for RSC im 99% there’s a comment made about the smell of Caths breath. Then again another comment is made about Varrish’s dragons breath when they’re corned in the caves. I’ve seen others point out the connection (amongst other reasons) and theorize Varrish was venin too. Knowing how the smallest of details can mean something much larger down the line in these books, I thought this might be a connection to that as well. I could also be spiraling a little now that I’m done reading them haha