The echidna penis is an oddity. Like some birds and reptiles, the penis is used ONLY for the passage of semen, all urine and stuff goes through the cloaca. And, like some reptiles, the penis of the echidna is bifurcated. That is, there are two "heads". Each of those heads is ALSO bifurcated, resulting in a total of four little heads (called, charmingly, "rosettes"). Not only that, the opening for the semen on each of those isn't a hole. No, it's more like a showerhead.
Their penises have four heads, but they only ejaculate through two of them.
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