Question re a string containing a regex

pwc299.raku

## Question: why do #s 1 & 2 work, but #3 does not?
##
my @w = <cat bat rat>;
my $s = 'the cattle was rattle by the battery';

say '1: ', $s.subst(/ <|w>( @w )\w* /, {$0}, :g);

## Output> the cat was rat by the bat



say '2: ', $s.subst(/ <|w>( cat || rat || bat )\w* /, {$0}, :g);

## Output> the cat was rat by the bat



my $re = '<|w>( cat || rat || bat )\w*';

say '3: ', $s.subst(/ <$re> /, {$0}, :g);

## Output> Use of Nil in string context ... (3x)
## Output> the  was  by the