Friendships are tested on Grey's Anatomy, Season 10, Episode 5: “I Bet It Stung.” And by "friendships," we really mean one particular pair of twisted sisters. Yep, that's right: Meredith and Cristina's everlasting bond will be strained in a big way when you tune in tonight.

How and why do our girls end up at each others' throats? And what other drama can we expect? We've taken a close look at the sneak peeks to see what they reveal about the episode.

Don't worry, spoiler-phobes, this one's for you — we won't reveal anything that's not in the sneak peeks themselves.

Meredith wants to dive back in with an old patient. In the sneak peek below (sneak peek starts at :31), Meredith is back to work, and she's excited that Cristina is operating on a patient Mer had seen before her maternity leave. As far as she's concerned, she should help with the operation, which is apparently some sort of super-tough liver and heart transplant.

Cristina's surprised. Cristina's surprised to hear that Meredith is ready to dive into the deep end, but ends up accepting her friend's offer to help — but points to an article about the specific kind of operation that she needs to read first.

Zola gets hurt. In the clip below, we learn that Zola has hit her head. While she's going to be a-OK, her daughter's dire situation distracted Mer, who's still learning how to balance being a surgeon and a mom.

Cristina replaces her with Bailey. Because she thinks Mer isn't 100 percent focused, Cristina's replaced her BFF with Bailey in the OR — and she's not sugar-coating the decision.

Mer is kind of distracted. While Cristina just throwing Mer aside without warning is a little harsh, it turns out she might have a point: Mer hasn't had time to read the article Cristina told her about. Bailey, on the other hand, knows what to do. It seems like Cristina may have made the right call.

Getting to know Alex's dad. In this final sneak peek, we get the rundown on Alex's dad, thanks to Jo. Based on this clip, he's a bit of a charmer.

He might be around for a bit. While Alex's dad's surgery is over, there are still some tests that need to be run, which should give the show plenty of time to up Alex's angst factor.

Alex denies his father. Joe, of course, wants to see Alex reconnect with his long lost father, but Alex isn't having it — he's afraid of how he'll react.

Are you excited for this episode? Sound off in the comments below!

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Catch the next episode of Grey’s Anatomy on Thursday, October 17, 2013, at 9 p.m. ET/PT on ABC.