The ocean-like sound produced by a seashell is an interesting phenomenon.
Orca Species in Adventures in Valerick TTRPG
Listening through the world of a sea shell! – Sound Xplorer
Notes from the Field
Why Do You 'Hear The Ocean' In a Seashell? - Coastal Care
A world of Faith, Airships, and Iron: setting historia/eventual ME cross?: Proof-readers wanted, Page 36
Why can you hear the sea in seashells? - Fun Kids - the UK's children's radio station