Tongue Fu: how to talk when you don't know what to talk

I don''t think so. Silence''s sometimes good but it is not for someone who is in any work relevant to doing services.
I only kept silence when I was deep in thought... and it''s too crazy to listen to others without saying anything. At least you should have some respone as: ''uh-huh?'', ''really?'', ''yeah!'', ''pardon!'',... or just nod your head.

So what is the differnce between saying nothing at all and "uh-huh?", "yeah", etc...? Please bear in mind that saying is completely difference from making a sound.

Uh-huh?