Dynamically creating a hash for keys()

[Jason Foster]

Can anyone help me to understand why this code refuses to compile?  
Even better, can anyone help fix it :)

    %hash = qw( fred filntstone barney rubble tom delong );
    print( keys( reverse( %hash ) ) );
The error message...
    Type of arg 1 to keys must be hash (not reverse) at ./killme.pl 
line 4, near ") ) "

... was pretty confusing since it implies that "reverse" is a type?!
I tried making an anonymous hash as follows...
    print( keys( %{ reverse( %hash ) } ) );
... but got no results at all.
Help!