The Hiso Hiso no Mi is an anime-onlyParamecia-type Devil Fruit that allows the user to understand the heart of an animal; in other words, allowing them to "speak" (without words, telepathically) to animals. It was eaten by Apis.
The power of the fruit was first demonstrated but not clearly explained during the moment when the Marines under Nelson discovered that Apis was aboard the Going Merry and began attacking the ship. The Devil Fruit's ability was shown inherently when Apis learned from the seagulls that a strong wind was coming their way which thus allowed the crew and her to escape from the pursuing Marines.
Hisohiso means "whisperingly" in Japanese, a reference to the voice the user can hear.
In the FUNimation dub, it is called the Whisper-Whisper Fruit.
In the Odex dub, it is called the Fruit of whisper.
Strengths and Weaknesses
While the fruit's power enables the user to telepathically communicate with animals, it should be noted that its influence does not extend to controlling the will of the animal nor the animal itself. There is also the curse of not being able to swim, like all other Devil Fruits. It is also unknown if the user can use the Devil Fruit's ability to call for help from undersea creatures in any circumstances.
Apis has been shown to communicate with animals with this power, and by earning their trust, they can warn her of any danger ahead of time. She used this power to talk to her dragon friend, Ryu.
The Hiso Hiso no Mi is one of the few Paramecia that has virtually no direct offensive uses.