Welcome to Half-Life Answers. What would you like to know?

A similar question was asked, and the answer was:

"This most often happens when the Zombine sees an enemy relatively close to it, in which case it will most likely pull out a grenade and charge. JgcxCub 16:18, March 13, 2010 (UTC). Also, if you shoot it a couple of times, it will get angry and/or scared and pull it out."