use feature qw[ say ];

use Safe;

# works here
say "Hello!";

my $cft = Safe->new;
# allow all opcodes
$cft->deny_only();

# doesn't work here (expected result)
$cft->reval( 'say "Hello Again!"' );

# explicit load of feature, but doesn't work (unexpected result)
$cft->reval( 'use feature qw[ say ]; say "Hello Again! 2"' );