Seriously? When you go to a zoo have you ever gotten closer than 50 feet to any animal except the goats in the petting zoo?
Since you asked...
A bird on my hat in an aviary, a lemur on my head, walkthrough ape enclosures... And the mountain lion and bobcat exhibits at the Dallas zoo (now demolished) used to have about a 10 foot spacing to the animals.
50 feet? You need to travel more.