I'd assume 'wildcat did growl' was chosen for for the use of staccato to create rhythm from the consonants, which would be absent with 'wildcat growled', rather

I'd assume 'wildcat did growl' was chosen for for the use of staccato to create rhythm from the consonants, which would be absent with 'wildcat growled', rather than to add more feet to the line, but hey, we are just layering ephemera on ephemera here.