The reptile named Janus, who lives in Geneva's Natural History Museum and has become the institution's mascot, was washed with a toothbrush on his special day.
Expert say the animal would not have survived predators in the wild because the two heads cannot be pulled into the shell for protection due to lack of space.
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Janus is fed with organic fruits and vegetables, cut into pieces.
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Other events to mark his birthday on Saturday included taking a "selfie with Janus," meet-and-greets with his caregivers, and a scientific talk explaining the oddity of Janus' two heads.