Perl's tokenizer classifies some keywords as "weak keywords" such that you can override them with user-defined functions. (Calling them is another matter.) delete is a weak keyword and each is not. our is weak, but sub is not:

use strict;
use warnings;

sub each   { warn 'main::each() was called' }
sub delete { warn 'main::delete() was called' }
sub dump   { warn 'main::dump() was called' }
sub chop   { warn 'main::chop() was called' }
sub our    { warn 'main::our() was called' }

my %person = ( name => 'Ken Takakura' );

while ( my ($key, $val) = each %person ) {
    print "$key: $val\n";
}

&our( $person{name} );
delete $person{name};
chop $person{name};
dump( $person{name} );
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I don't know how to make a list of weak and normal keywords without reading the source code (keywords.c or regen/keywords.pl).