There is a plain text file on Unix-like operating systems called /usr/dict/words, which contains an alphabetically sorted list of (on my machine) around fifty thousand English words and names. Since Perl is so wonderfully suited to munching text and manipulating strings, it is just the tool to do weird and useless things with the dictionary file.
Here are some examples:
A password cracker
words whose reversals are their opposites
one handed words
Cheating in Crossword puzzles, Scrabble, target and other word games. See Five-letter scrabble words.