In Hartings' opinion the fry/Frosty appeal is just as much about culture trends as taste.
"I'm from Ohio [where Wendy's HQ is located] so I might be biased, but this is certainly something that I grew up with, I have very clear memories of doing this as a kid. Sure, there are molecular underpinnings as to why salty-sweet combos work so well, taste-wise, but the real appeal here might be something different, it's a culture thing."
Hartings thinks the social science behind this decades-long movement is just as influential as taste. When trends like this -- especially "secret menu hacks," as they may be lamely called -- steamroll into popularity, one person sees someone else doing it, and they want to do it too.
People are sheep! This is how phenomena are born. Good ideas spread like herpes in clothing-optional saunas.
Nowadays, it's just as likely that one person will see someone else tweeting about their Frosty/fry endeavors as actually doing it. According to Wendy's HQ, there are an average of 21 tweets per day about dipping fries into Frostys.
"In the digital age, this all kind of took on a life of its own on social media," said BryAnn Roth, Manager of CSR & Brand Communications for Wendy's. "But we really never used it in wide-spread marketing materials… we've never really had to. This is something people are just going to do. They've always done it. And now, they are posting about it."
"The classic diner experience really fueled this. You would order a shake. Your friend would order fries. You guys would end up sharing everything, and naturally the fries would end up in the shake," Hartings said. "Even if there's not a precedent there, it's a very natural reaction, and it's an interpersonal way to eat -- which is usually in a social setting, anyway."
So in a way, the hard science of taste (salty plus sweet!) works in conjunction with the social science of popularity and fads to create a bona fide fast-food phenomenon that's better suited to experience than explanation. You need to try it to understand.
When Thobe wears one of her company-provided shirts to the supermarket, she usually doesn't get stopped by gushing fans. When she wears her "Frosty + Fry" shirt (yes, they give those out to employees), she can barely walk 5ft without being drawn into conversation.
"Some people stop me and tell me they can't believe they haven't thought of it yet. Others stop me and tell me it's pretty much their favorite thing ever.
"No matter what, it gets a reaction, though. And that's how you know it's something special."