s/^          # Start of string
  (          # Start remembering
    \W*      # Leading non word characters
    (\w+)    # First word of string
    \s+      # Whitespace
    (\w+)    # Second word of string
    \b       # Make sure we got the entire word
    .*?      # Skip till second occurance
   )         # Stop remembering
   \b        # Start at the beginning of a word
   \2        # Repeat of the first word
   \s+       # Whitespace
   \3        # Repeat of the second word
   \b        # And that's the end of the word
 /$1/sx;     # Just keep what we remembered