Guests on a whale-watching tour squealed as several humpback whales slapped their fins, making waves during an encounter in Cape Cod Bay, Massachusetts.Footage recorded by Ken Grille with a zoom lens shows the moment the whales rocked a nearby fishing vessel as they struck the water with their massive fins, much to the delight of the viewers on his tour.“Imagine you are out there on a relatively small boat, fishing with a few buddies, and this happens. Multiple humpback whales emerge just a few yards from your boat and of all things they begin fin-slapping behaviors. Craziness,” Grille wrote. Credit: Ken Grille via Storyful