The party discovered several bone whistles during their investigations into the King in Yellow.

• A cord similar to that used to tie a whistle was taken from the murderer of Doctor Lionel Trollope.

• One was dropped by Lawrence Bacon shortly before he fell into the canal, this whistle appears to be carved from black-stained bone. It is threaded onto a leather bootlace. the whistle is carved into the likeness of one of The Springer Mound Monsters wrapped around the shaft of the whistle.

• A very similar whistle was carried by Henry Lister on the train to Inverness. After being dissuaded from continuing to Scotland Lister left the whistle behind with the investigators. He said that the whistles could be used to call or control 'the Children of Hastur', but that he had no idea how to use his and had never encountered such a creature. It seems that the cultists have these whistles as much as tokens of membership as for any practical purpose.

• A room full of similar whistles were found in the Sculpture Museum in Carcosa, as the Investigators searched for Alexander Roby.

• Doctor Barlett suspected Alexander Roby used a whistle to summon the creature that killed his sister and father.