"There are going to be people who say 'okay, your samples prove that those samples are bears, but you can't prove that there aren't yetis'," Lindqvist says. So yes, she admits, we're never going to be able to 100 percent prove that yetis do not exist, period, end of story. That's the tricky thing about cryptids. Science simply can't say that something is definitively untrue. You can't prove a negative. The absence of evidence is not evidence of absence, and so on. This allows wild theories and preposterous ideas to thrive based on the premise that no one can ever truly say they're wrong.