Ruminatively means “in a deep, careful, slowly-thinking way.” It is the adverb from ruminative, so it tells you how someone does something: she spoke ruminatively; he stared ruminatively at the rain. It has the same quiet, bookish flavour as the adjective. You will almost only see it in writing. In serious prose it does not mean “like a cow” as a joke, though the picture underneath is still that slow second chew. Use it when the thinking itself is the point of the sentence.

沉思地、反覆思索地