Making Silent NPC's

How can I make it so when I spawn certain NPCs with lua they won’t make noises or talk? Like NPCs such as Vortiguants and Zombies. I think if I made my own SNPC I could control that and it’d also be helpful so I could animate them too. But I was looking at this guide http://wiki.garrysmod.com/?title=Basic_Scripted_NPC and was kind of confused and didn’t really see anywhere I could configure it to my needs. Could someone please help me?

Can anyone help me here or at least point me to a different guide on making SNPCs?