they called, I picked up, silence on the other end for a few seconds then they hung up

Pond Scum! Tele-marketers. They call, call, call, call and call again. No msg. is ever left. It's not a known number so I do not pickup. They have called multiple times. Low life Bottom feeding Pond Scum. Blocked.... bye bye Pond Scum!

Unfortunately I picked up.  Silence... and then hung up.  They're just fishing for numbers that answer so they can re-sell your number to other callers.  They're also learning in the process - what area codes you are more likely to pick up, what times of the day, after how many rings.  All of this is worth money to other companies that now will be calling me.  Yeah, of course I blocked the number, but that won't make any difference since it is MY number that is being commoditized.