save in /tmp, and run emacs -Q -nw /tmp/r.pl

Now move the cursor down and attempt to change shttp to s[http .
As you insert the [ an infinite loop begins.
You probably can break out with a C-g, but you might need a
$ killall -HUP emacs

In GNU Emacs 24.0.50.1 (i486-pc-linux-gnu, GTK+ Version 2.20.1)
 of 2010-12-14 on elegiac, modified by Debian
 (emacs-snapshot package, version 1:20101212-2)

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: C
  value of $LC_CTYPE: zh_TW.UTF-8
  value of $LC_MESSAGES: C
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: C
  value of $LANG: zh_TW.UTF-8
  value of $XMODIFIERS: @im=SCIM
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t