I quickly realized that you omit any of the code in the main program.

Well that shouldn't take me too much more work, I'll just see what you wrote (something about text files), and see if I can cobble together something small that calls slow_print.

Then I looked at slow_print, and saw that it depends on an externally defined array called @paras, an external variable $rewrap_margin, and at least two external subroutines, rewrap and handle_keystroke.  (By "external", I mean external to what you gave us; maybe in the main program or some library?).

My point is, I've now lost interest.  There are plenty of other questions where the poster is giving enough information for me to get to the fun stuff; the actual sleuthing of the problem.  To do that with your code one has to anticipate the definitions of two other data structures and two other subroutines, as well as guess how you might have called this subroutine.  Sorry, but that's work!

Please consider providing a small, standalone program which runs on its own, and illustrates the problem.  Then I'll be glad to come back and take a look, knowing that I can dive right into solving the problem.