Dead Dogs and Cats

So, being the history buff/geek that I am, I am currently reading through Page Smith's A New Age Now Begins: A People's History of the American Revolution. It's an excellent read, but I came across a strange excerpt the other day that continues to capture my attention. It's about the everyday common Englishman's reaction to the resolution of the First Continental Congress:

When the hangman and two sheriffs appeared in the Royal Exchange to burn publicly copies of the journal called Crisis, which espoused, among other things, the cause of the colonists, the fire was immediately extinguished by the crowd, and the officers were pelted with dead dogs and cats.

So here's my question: Were there just dead dogs and cats randomly lying about, or, when someone's dog or cat died, did they hold on to them, say in a box by the front door, just in case they needed to pelt someone with them? This has me in a quandary.