When I was a kid, I remember walking through a Ripley's Believe It or Not museum. Since I was at an impressionable age, what we saw all seemed pretty believable to me but my parents were a lot more skeptical.
It's hard to gauge whether I'd feel like them now because I honestly don't remember most of what I saw in there. However, what does stick out in my mind was a two-headed sheep that they had on display. I suppose that if there was anything I had a hard time believing, it's that such a creature could exist.
Of course, I now know how possible it really is and why I never saw any two-headed animals outside of that museum. And the realities I've since become aware of make one specimen all the more rare and special.