Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
rūmĭgo, āre, v. a. [rumen-ago], to chew over again, to ruminate: jam tertium qualum, App. M. 4, p. 153, 2: bos si non rumigat, Gargil. Mart. Cur. Boum. § 15.