This is broken, notice that it just prints the first element of the @test array? So aplaca doesn't print. In fact if you put peguin as the first element of test it prints peguin. The problem is that you're trying to be to terse. The $_ that you're using in the grep is not the $_ that aliases an element of @test, it's the $_ that aliases an element of @redundant (grep uses $_ too). So you're saying next if there's an element of redundant that matches an element of redundant. Probably not really what your were thinking of.
Update: Well, it was broken. I started getting down votes for this node, I guess 'cause it's no longer applicable.
"So... What do all these little arrows mean?"