How are the rattles on a dusky pygmy rattlesnake different from the rattles of the canebrake or diamondback rattlesnakes?

Dusky pygmy rattlesnakes rattles are tiny, barely audible, and sound like a buzzing insect. 

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Photo: (Diamond back rattlesnake, State Archives of Florida, Florida Memory, http://floridamemory.com/items/show/149281)

Question from The Florida Quiz Book by Hollee Temple