It doesn't though, because you are doing the substitution four times on each element, thus introducing a nice echo effect.

knoppix@Microknoppix:~$ perl -Mstrict -wE '
> my @pack =
>    map {
>       my $suit = $_;
>       map qq{$_$suit}, qw{ J Q K A };
>       } qw{ H C D S };
> my $n = 0;
> while ( $n < 4 )
> {
>     foreach ( @pack )
>     {
>         s/C/Clubs/, s/S/Spades/, s/H/Hearts/, s/D/Diamonds/;
>     }
>     $n ++;
> }
> say qq{@pack};'
JHeartseartseartsearts QHeartseartseartsearts KHeartseartseartsearts A
+Heartseartseartsearts JClubslubslubslubs QClubslubslubslubs KClubslub
+slubslubs AClubslubslubslubs JDiamondsiamondsiamondsiamonds QDiamonds
+iamondsiamondsiamonds KDiamondsiamondsiamondsiamonds ADiamondsiamonds
+iamondsiamonds JSpadespadespadespades QSpadespadespadespades KSpadesp
+adespadespades ASpadespadespadespades
knoppix@Microknoppix:~$
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I hope this is helpful.