This is an excellent question since "swamp adders" (or snakes) do not have external ears, but I am certain that the intent of the whistle was to recall the reptile to its owner.
In 'The Adventure of the Speckled Band,' there was a whistle then a clanging noise, and they were caused by the whistle that Dr Roylott used and the closing of his safe door.
The father was murdering the daughters by transferring a poisonous snake through a ventilation system and calling it back with a whistle.
a speckled band
The antagonist for "The Speckled Band" was Dr. Roylott.
If you read the story, you will discover that what they think is a band, is actually a poisonous snake.
'Oh, my God! Helen! It was the band! The speckled band!'
it is a swamp adder- a type of snake
Helen heard a low whistle followed by a clang and a metallic clatter on the night her sister died in "The Adventure of the Speckled Band." She described the sound as "horrible, eerie, and unnatural," contributing to the mysterious circumstances surrounding her sister's death.
The Speckled Band
The Speckled Band - 1923 is rated/received certificates of: UK:U
They like to eat other snakes by dakota