Whistle snorkel for dolphins

I run a boat business taking tourists for snorkel rides with wild dolphins. When we get close to the dolphins we ask the tourists to sing or hum through their snorkels to signal playtime. A customer once suggested to create a snorkel with a whistle at its top. I've never seen such a product but I think it's a good idea. It's not difficult to make and dolphins tend to respond well to the sound of a whistle.

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