Orca Keeps Circling Boat, Then A Passenger Sees What’s On Its Back

Rhythmic hammering

And then they heard it. A low, rhythmic hammering, almost felt through the hull as much as heard through the air. Tom cut the engine slightly, and the sound became clearer.

It was coming from around the next point of land, where a rocky headland blocked their view of the coastline. The orca swam sight toward it.