Couple see shoe box along street in NYC

My girlfriend and I were walking in the West Village in Manhattan when we saw a crisp Nike bag that looked brand new. I love a good NYC street find so I looked and there was a shoe box inside! I thought I was getting a new pair of Nikes when my girlfriend noticed writting on the box. It was a goodbye letter to a pet in kids handwriting. Based on the weight of the box my guess is guinea pig.