What should I say to a guy when it sudenly gets quiet?

I would suggest that you ask him something that you know is of interest to him and make him feel good about himself. Questions always a the conversation going. But don't ask something that only requires a yes or no answer. Example: How did you ever learn to throw the football (any sport( so good? Or, I'm spending as much time at the beach this summer, as I can, how about you or will you be doing something else? Or, how's that new job going that you recently started, and what do you do? I like the way you're having your hair cut now, what made you change? Get the idea?

i agree with hercules but to add sometimes as guys we don't have anything to say we are not like women. sometimes we just like to enjoy a quiet minute with the beautiful girl next to us. or we are building the confidence to steal a first kiss or distracted by events of the day.

Aside from me not understanding why you posted this question as anonymously.

It really depends on the situation. If you just told him you loved him, and everything goes dead quiet, what you say then might be different if it went quiet because you farted. (Sorry, vulgar, but a valid point)

You have to gauge the situation and determine the best course of action. Sometimes stupid humor is the best decision. Sometimes apologies, and sometimes just bringing up a different subject.

Was there a specific incident, or are you just asking a random question?

i had the same problem . when it got quiet I felt like I just have to say something. don't think about what you should say or not. just wait and see when or if he is going to say something .
with my current boyfriend I learned how to enjoy being quiet, I don't care anymore when its quiet and its not weird at all