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Does this Aston Martin V8 Vantage make your mouth water? (courtesy of flickr user Destinys Agent)

If you think about it, some of the phrases we use to express desire for inanimate, non-food items are pretty weird. We “drool” over cars. Our “mouths water” at the sight of a pile of money. Salivating makes sense when we’re talking about food—after all, salivation is part of the anticipatory phase of digestion, and saliva moistens our food to assist swallowing—but why would we drool over something we can’t eat? We do, though, as shown in a new study in the Journal of Consumer Research.

David Gal, a marketing professor at Northwestern University, conducted two experiments, each time measuring saliva production. In the first he started off with a writing assignment, asking the participants to write about either a time they felt they had power or a time when they lacked power. Those two groups were then split and shown either images of money or, as a control, office supplies. Only the people who had been assigned to write about a time when they lacked power salivated at the sight of money, Gal found. The assignment had primed those individuals to find money to be more attractive. (Office supplies, not shockingly, had no effect.)

In the second experiment, which focused on the responses of men only, the participants were primed with what Gal calls a “mating goal.” Half had to choose a picture of a woman and write about an imagined date with her; the other half had to choose a picture of a barbershop and write about an imagined haircut. The images of money and office supplies were then replaced with pictures of sports cars and fastening tools. Again, the participants who had been primed to think about what they lacked salivated over the photos of the cars. (Guys really do think that sports cars make them more attractive to girls.) “These findings show that exposure to a material reward cue stimulates salivation when the reward value is high,” Gal writes.

OK, so under the proper circumstances, we might drool over a non-food item. But why would this be? As Gal notes, “Salivation to material reward is not of any obvious function.” He has two theories, though: One, that we are conditioned from early in life to associate material rewards with food. More likely, though, might be number two, that salivation is a side-effect of the natural reward system. If there’s just one system in our brains that rewards us for everything—from drugs to money to chocolate chip cookies—then it makes sense that we could salivate over any of those things. As Jonah Lehrer writes on the Wired blog Frontal Cortex:

Although our dopamine neurons evolved to process and predict biological necessities, they’ve since learned to embrace a more catholic set of desires, so that pieces of green paper filled with pictures of dead presidents get them very excited. While relying on a single pathway to process all of our rewards normally works quite well—the dopamine reward pathway is some well-tested cognitive software, since the same basic code is present in nearly every mammal—it does lead to a few unintended side-effects. Just ask a drug addict, or that man who starts to drool whenever a Ferrari drives by.