A Soviet scientist in the 1950s transplanted an extra head onto a dog!

Russian surgeon Vladimir Demikhov was an early pioneer in transplant surgery. His work with dogs lead to one of the first successful animal heart transplants. After that, he grafted a puppy’s head and front limbs to an adult dog, making a two-headed dog! The animals lived for 6 days together, sharing a heart and body. The two heads had completely different personalities. The puppy actually still acted like a puppy.
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