You've probably seen examples of assigning to a hash that look like this:

my %favs = (
    syfy     =>  'Babylon 5',
    fantasy  =>  'Lord of the Rings',
    animated =>  'Monsters vs. Aliens',
    anime    =>  'El Cazador de la Bruja',
    );
[download]

That is exactly the same as:

my %favs = (
    'syfy',     'Babylon 5',
    'fantasy',  'Lord of the Rings',
    'animated', 'Monsters vs. Aliens',
    'anime',    'El Cazador de la Bruja',
    );
[download]

Which is the same as:

my %favs = ( 'syfy',  'Babylon 5', 'fantasy', 'Lord of the Rings','ani
+mated', 'Monsters vs. Aliens', 'anime', 'El Cazador de la Bruja', );
[download]

So => is the same as a comma!! The only difference is that with => the operand on the left can be a bareword (i.e. does not normally have to be quoted). So that hash assignment is really just a list. And since perl is looking for key/value pairs the number of elements in the list has the be an even number.