Any of these enchanted inflatable sea captains can be heard by pulling the cord.

One of these was used by the Griff to retrieve the Coconut of Quendor from the mouth of the Watchdragon. After being plugged and inflated in one of the sleeping dragon's nostrils, the entire head lifted out of the water. The Griff tied the captain's leg to the inflatable raft carrying the Coconut, then popped the captain with one of the dragon's teeth. This spewed the captain out of the dragon's nose, towing the raft behind. When the deed was finished, this inflatable captain lay abandoned in the waters of the Great Sea, never to be inflated again...

SOURCE(S): Zork: Grand Inquisitor