What is the animal in our apartment--could it be snake?

In the morning, we found a piece of fecal (Feng bian in Chinese) as big as 1/4 egg in yellow color in our living room near air-conditioner (which drops water at work). This is the second time since we found it. What could be the animal who produced that. Is it a mouse or a snake... so scaring.... and I also don't know how it sneaked into our home.
Our home is an aprtment in New Jersey.

Any body has any idea or suggestion? Thanks for sharing.......