Remember the "Ballad of the Crystal Ponies"?
Fluttershy sings the line "They had a petting zoo with tiny ewes."
What if this book, being old, isn't an exact translation, and "Petting Zoo" is actually a euphemism for a brothel. You know, like the other definition of petting:
Phrase used in old-fashioned teen sex manuals for foreplay without intercourse.