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Free food at work might seem like an awesome office perk, but it may actually be a sort of subtle psychological warfare.

In a recent write-up, the BBC looked into whether well-fed workers are happy workers. Of course, employees like getting free stuff from work, but that stuff comes with a price. Free food is one of the prime examples.

For instance, a manager at Google—the gold standard of free food at work—admitted that lines at cafeterias aren’t always caused by demand. Wait times are “purposefully kept above a certain length to encourage ‘serendipitous interaction’ among staff, hopefully leading to creative discussions.” Believe it or not, Google is purposefully wasting employees’ time to make them mingle.

But for the tech giant, wasted time at the office beats time at home. “Google, in particular, provides everything and that’s designed to keep you there,” the BBC quotes Sandi Mann, senior psychology lecturer at the University of Central Lancashire, as saying. “At the extreme it makes you feel you need never go home. It’s a perk and people feel they want it. But it’s not a good thing if it means you haven’t got a life outside.”

Other manipulative techniques seem more like bad dating advice than proper office etiquette. For instance, experts advise against a steady stream of goodies, instead encouraging companies to play hard to get. Pamela Yow, a senior lecturer in management at the University of Kent spoke about how everyday perks such as coffee will eventually lead to complicity. “If [perks are] unpredictable and people are told it’s because you’ve had a fantastic month, it’s a lot better,” she said.

Not to say that eating an office doughnut means you’ve sold your soul to the devil, but the big takeaway is to be mindful of how you keep your office life and your personal life separate. You wouldn’t replace your dining room table with a work desk, would you? Though it probably wouldn’t kill you to clear all those work papers off your table so you could eat a proper meal at home for a change.