For those who don't know, "how the cow eats the cabbage" (a/k/a "how the cow ate the cabbage") is a common saying among rural folk. My late wife, who grew up on a remote Arizona ranch, used to say it all the time. It usually seemed to be used in the sense of "I'm gonna have to set that fool straight on how the cow ate the cabbage" or "good grief, you'd think by now the idiot would know how the cow eats the cabbage." See, you learned something today!
Here's a similar tidbit you may not know: Many people attempted to invest the REM song "Losing My Religion" with deep meaning. Michael Stipe explained that "losing my religion" is just a Southern expression like "well, shut my mouth." As in, "When I saw Shirley's new hairdo, I dang near lost my religion." You're welcome.