It's not only the postman who knocks twice.
Goldman Sachs does too, following its recommendation earlier in the week to take profits on commodities with an even more bearish one, to go underweight.
In fact, agricultural commodities were spared the investment bank's wrath. Goldman said that low stocks would keep prices of the likes of corn and, especially, soybeans, supported.
But after the commodities sell-off that Goldman's first report caused, or at least was blamed for, the latest briefing presented a negative backdrop to Friday.
"The bull commodity story is losing momentum," broker US Commodities said, noting the determination by China to get its higher-than-expected inflation, revealed today at 5.4%, under control.
"China and other countries are trying to stall food inflation. You have to bet they get it done.
"Interest rates around the world are rising." And that implies lower economic growth, and a setback to demand for raw materials, right?
Furthermore, the US Department of Agriculture's idea that livestock farmers might switch from corn to wheat is beginning to be taken more seriously.
"Corn is now challenged by future wheat feeding as soft red winter wheat [the type traded in Chicago] has gone to a discount to corn," US Commodities said.
Corn remained at a premium on Friday, but not by much, after falling 1.1% to $7.45 ¾ a bushel in late deals.
Chicago wheat was 0.3% higher at $7.43 a bushel.
At least wet weather was in corn's favour, potentially slowing spring sowings, and helping the new crop December lot add 0.5 cents to $6.56 a bushel.
Darrell Holaday at Country Futures said: "The wet conditions and forecast in the Midwest are leading to another significant round of liquidation in the bull corn spreads." That is an unwinding of a strategy of buying the short-term lots, and selling those further ahead.
"There were just way too many people in that spread and they need out. Look for it to bottom today or Monday."
The wet weather remained, however, a setback to prices of Kansas-traded hard red winter wheat which, promising some relief to a crop badly needing rain. Kansas's May lot eased 0.1% to $8.63 a bushel.
Chicago's May contract stood 0.4% higher at $13.36 ¾ a bushel with half an hour of so of trading to go.