First of all, I'm sorry for the unspecific title, but since I don't know what it is called, I cannot specify.
I'm regarding the last bar before they key switches from Eb Major (2 b) to C Major (no alterations). Above the g, there is some sort of diamond-shaped note.
Edit: Here is a link to a recording available on YouTube. The thing that I refer to can be heard at about 1:28.