"I run yards like Swiss chard," said Cook after totaling 226 yards and four touchdowns in a win over the Green Bay Packers. "That's what it is."
It turns out that expression is not standard nomenclature for Cook, but rather a line fed to him by producers of "The Tonight Show with Jimmy Fallon."
The popular late-night talk show asked the likes of Cook, Tampa Bay Buccaneers tight end Rob Gronkowski, Tennessee Titans quarterback Ryan Tannehill, Seattle Seahawks wide receiver DK Metcalf and Los Angeles Rams cornerback Jalen Ramsey and others to slip "nonsense phrases" in during their weekly media availability for a segment called "Drop It In."
Gronkowski made headlines for comparing his chemistry with Tom Brady to drizzling maple syrup and invented an elaborate backstory when asked to clarify what he meant.
Cook used his phrase twice and remained stone-faced while answering so he did not draw attention to the prank.
After a video mash-up of all the responses was posted on "The Tonight Show's" Twitter and Instagram feeds, Cook let everyone in on the joke.
"They gave me a script and there were some lines that I had to pick from," Cook said on Wednesday. "I thought that was the best one coming off the game we had. I had to come up with -- how can I throw this in there without anybody catching it? And that was the hard part. I had to keep a straight face because I didn't even know what it meant, either. It was crazy."
Cook says he still doesn't know what "Swiss chard" is.
"I think they gave me the line about the maple syrup, the one Gronkowski used," Cook said. "But it was like, I'm a running back, so I'm running yards, so this is the best one for me. It's funny though."