Over in Obfuscation this point came up:

C:\>type test.pl
use, strict

C:\>perl -MO=Deparse test.pl
syntax error at test.pl line 1, near "use,"
test.pl had compilation errors.

C:\>test.pl

C:\>type test.pl
use => strict

C:\>perl -MO=Deparse test.pl
'???', '???';
test.pl syntax OK

C:\>
[download]

Now this is of course pretty arcane but what is the difference and why?