Where wolf's ears are, wolf's teeth are near.. - Völsunga saga

Like the updated quote of 'loose lips sink ships"

I think they both apply to knowing who is listening in. Plot and intrigue during the Viking times and earlier times were mostly of an internal nature of an insider working for themselves or for someone else. When you find the listening wolf ears it is prudent to be ready and prepared for the wolf.

Today there are so many wolves at the doorsteps it is hard to protect oneself from them.