While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a closer look at particularly stock-shaking upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Kellogg (NYSE:K) slipped 1% this morning after Deutsche Bank downgraded the cereal giant from "buy" to "hold."

So what: Along with the downgrade, analyst Eric Katzman lowered his price target to $65 (from $68), representing about 4% worth of upside to yesterday's close. While contrarian investors might be attracted to the stock's recent sluggishness, Katzman believes that Kellogg's appreciation prospects remain highly uncertain given its lack of visibility.

Now what: Deutsche sees Kellogg's risk/reward trade-off as pretty balanced at this point. "While we believe Kellogg's 4-yr restructuring is logical and necessary, limited 2014 visibility into sales/EBIT recovery and heavy cash cost push us to a HOLD opinion," noted Deutsche. "LT growth in global cereal and snacks are compelling but it's clear greater investment is required." When you couple that uncertainty with the stock's 10-year-high P/E of 24, it's tough to disagree with Deutsche's downgrade.