In perl, you can increment strings.
$a = "a"; $a++; print $a; #results in 'b'
OK, a little weird, but simple enough. But:
$a = "z"; $a++; print $a; #results in 'aa'
$a = "ç"; $a++; print $a; #results in 1
Hmm. Not unicode safe…
$a = "14"; $a++; print $a; #results in 15
$a = "14 bucks"; $a++; print $a; #results in 15
$a = "fourteen"; $a++; print $a; #results in 'fourteeo'
Uh oh. What about decrements?
$a = "14"; $a--; print $a; #results in 13
$a = "14 bucks"; $a--; print $a; #results in 13
$a = "fourteen"; $a--; print $a; #results in -1
Boom! (Decrementing strings isn’t supported, but at the same time perl tries to be clever with identifying numbers in strings, so you might get the wrong impression.)
EDIT: Oh, and:
$a = "fourteen and change"; $a++; print $a; #results in -1
No spaces allowed.