Take over a Bash-process.

Hi!
I'm not really sure if this is the right forum to post this thread in but I'll try anyway.

I was just wondering if it's possible to "take over" a Bash process?
For example, if a user is logged in to my server (where I'm root) can I then somehow "clone" his session so I can see what he's writing and stuff in real-time?
Just like screen work, only he doesn't know about it.

The /proc directories for the user process have that a lot of that infomation.
Try info proc or man proc. I am assuming Linux becuase you mentioned bash.