You do not have to fill in the silences. My general observation is that, even with first time acquaintances, we can wait 4 whole seconds without a sweat in silence. This may be difficult at first, but you will get used to it. Let us breathe and get a moment to take it all in and then organically come up with the next comment or message or whatever observation. But during that silence, please don’t intently stare into the eyes of the other person. This may freak us out and instantly freeze us.