Just for completenes -

say "%hash"; should have the exact same effect.

Arguably it should, but it doesn't. A hash (or a construct with sigil %) is never interpolated in double quoted strings or qq(). I guess it is because, at list expansion of a hash, the sequence of key/value tuples is random. And then, the char % is meaningful for sprintf. However, hash slices are interpolated (their sigil is @). So,

my $hash = \%hash;
say "5: %$hash";
say "6: @hash{keys %hash}";
say "7: @$hash{keys $hash}";
[download]

5: %HASH(0x1185900)
6: Michelle Austin 22
7: Michelle Austin 22
[download]