Fun Fact about Yellowstone National Park: The animals living there are wild. One tourist was either unaware of that interesting tidbit, or didn't care, because they were spotted petting a wild bison. Luckily for this individual the bison allowed it without aggression. And lucky for future visitors as well, as injuries could result in safety measures that could take away from the Park's natural beauty.
Another interesting fact: certain animals can extend the gestation of their embryos. A wallaby took advantage of this evolutionary trait; the father of the new joey had left the zoo a year before its baby left the pouch.