Rob Kardashian took a break from his In 'n' Out runs to tweet at his sister Kim Kardashian. It looks like a cute exchange but we have a feeling something far more mean-spirited is afoot!

Yesterday, Kim wrote, “Wait wait wait I thought this nausea thing was supposed to be gone by now!!!! UGHHHHHH." Today, Rob broke his social media silence and replied, “@KimKardashian I sent u that voice note. It should help."

Kim replied, "Should I post it? I think people would love to hear the voice notes u send me!”

Aww that's cute, right? Or is it?

Rob then quoted Khloe Kardashian's ex French Montana's song "Hard Work" when he tweeted the lyrics at his big sis, “@KimKardashian HARD WORK GONE PAY OFF!! I BE HIGH OFF THIS MONEY I DUNNO WHAT THEY BE ON!!”

Rob's response makes us suspect that these two are just having a passive aggressive Twitter fight that we aren't in on. Three months ago, Rob compared Kim to the “b*tch from Gone Girl” on Twitter -- so we know these two have a strained relationship. It's possibly that the dueling siblings have kissed and made up but it's a lot more likely that Rob's been leaving harassing messages to his sister and this is Kim's passive aggressive way of threatening to release them. That seems a lot more plausible to us than the two of them being besties!

While we don't know if he's being sweet or trying to stab her in the back -- we have a feeling Rob's motives aren't entirely pure. Maybe next time Kim sees Rob, she should just get on his good side and bring him a Double Double?