Mine do it every couple months. They let out a blast like a volcano then "dribble" for 10 minutes or so then blast again. It goes on for up to an hour. Mine dont release eggs though. Maybe we should hook these nems up..lol. Here is a short vid of mine "dribbling".
<iframe width="480" height="390" src="YouTube - maxi mini nem" frameborder="0" allowfullscreen></iframe>