On Thursday the duo took the Best Friends Challenge—where one person has to guess what answer the other person would give to personal questions.
Grande had the first question: "If I could be any animal which one would I be?" Fallon thought he had this one in the bag by guessing "kitty cat," which makes sense considering Grande's style history. However, the singer surprised everyone with her answer of "seahorse."
"You wear cat ears all the time," Fallon said.
To that, Grande had a reasonable answer: "You can't wear seahorse ears, like, what are those?"
The next question for Fallon was, "What food do I hate most?" Grande seemed to know what it was and Fallon assumed she had gotten his "vibe." But their vibes must have missed a connection because the host wrote "mayo" while Grande guessed "mustard."
"Mustard? Mustard is so delicious. It's yellow, it has spices in it, it's vinegary!" Fallon said.
"I was close, though! It was in the condiment family," Grande said.
Grande's next question seemed like a given for Fallon: "Who was my first celebrity crush?" Fallon got a huge smile on his face.
"This is a little embarrassing to actually write it down," he said. "Everyone kind of knows." Oh, Jimmy. The actual answer? Grande revealed her first crush was "Jim Carrey." Fallon then proceeded to tear up his sheet that said, "Me."
"I was very close," he said sadly.
Watch Grande play the Best Friends Challenge—and find out her guess for Fallon's most embarrassing bad habit—in the video at top.