The animal kingdom features a wide variety of penises that vary in shape, size, and function. These are some of the most unusual of them.

1. Whale

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It’s only natural that the biggest animal would sport the biggest dong. Whale penises are so large that they’ve possibly been mistaken for sea monsters. Their erections can stretch up to 10 feet in length and ejaculate five gallons of semen in one shot.

2. Duck

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Argentine lake ducks use their corkscrew penises like a lasso to pull in females that they’re mating with who are trying to escape. Their 17-inch members are the longest bird penises ever observed.

3. Alligator

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Most animals should call a doctor if they have an erection that lasts more than four hours, but alligators don’t experience priapism in the usual manner: They have permanent erections and they hide their boners inside their bodies.

4. Echidna

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Echidnas belong to a rare group of mammals that lay eggs, and biologists say that their reproductive systems have more in common with birds and reptiles than with other mammals. Also, the penises of these spiky little creatures have more heads than Cerberus. Male echidnas have four heads at the end of their genitals, but none of them are used for urination (that passes through a cloaca).

While it's still a bit of mystery as to why they have four heads, a recent study did determine how they function: The urethra and the main blood vessel of an echidna's penis split into four parts, one for each head. Meanwhile, the corpus spongiosum—the penile tissue that moves semen through the urethra—is split into two parts, one for each pair of heads. But since only one corpus spongiosum operates at a time, the animal technically has two two-headed penises, which might give them a mating advantage due to their super productivity.

5. Slug

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Leopard slugs have penises that come out of their heads, and since they are hermaphroditic, both slugs can bear offspring when a pair mates. According to limacologists (an amazing word for scientists who study slugs), leopard slugs mate by hanging upside down and wrapping their gooey penises around each other.

6. Barnacle

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Barnacle penises can stretch up to eight times the length of their bodies—and unlike animals of other species, they can also change shape. Researchers in Alberta, Canada, found that barnacles that live in gentle waters have long, thin penises that are good for reach, while those in rough waters have short and wider penises that are better for holding off strong waves. The researchers then transported rough water barnacles to calmer waters and vice versa and found that after being moved around, the barnacles adjusted their penis's shape to better fit their environment.

7. Snake

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Like a good s'mores poker, snake penises have two prongs. Known as a hemipenis, scientists have speculated that snake penises developed in a double-branched way due to the location of their cloaca, which is at the base of the tail. Typically, a snake keeps its hemipenis tucked inside its cloaca, which can change the tail's shape (and make it easier to identify which sex a snake is from afar).

8. Cat

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Felines have barbs on their penises, which makes mating painful. Because cats aren't born with these fish hook-like features, a male feline who is neutered before he reaches puberty (which occurs around 6 months old) will never develop barbs. If a cat is neutered after puberty, the barbs will disappear within a few weeks.

9. Bee

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The greatest moment in a male bee’s life is the few seconds that he gets to mate with a queen. After that, it’s all downhill. Following the coitus session, the male bee’s penis gets ripped off and he dies shortly after.

10. Spider

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Male orb-weaving spiders come equipped with detachable penises. These spiders also practice cannibalistic mating, so breaking off your member can be a handy trick for a mate who is about to get eaten. Even after it's detached from its original body, the spider’s penis continues to pump sperm into the female.