Ian: What? No! Really?
Jeremy: Mum should have told us. I feel cheated!
Alexa: They think they're charming.
A Twin Trope. The tendency of twins to banter with each other. This includes Finishing Each Other's Sentences and feeding each other lines, among other things. A common trait of Single-Minded Twins and Twin Telepathy.
This can also be done by Those Two Guys.
Truth in Television, especially with twins of the same gender, as sharing one room and being in the same grade means they spend much more time together than average siblings. For that matter, some sets of twins develop a language specific to themselves that no one else understands. The technical term for this is cryptophasia.
- Bakemonogatari's Next Time On sequences are rapid-fire, seemingly random exchanges between Tsukihi and Karin, the main character's younger sisters.
- America and Canada get to do this occasionally in Axis Powers Hetalia, when they're alone together and America happens to remember he has a brother. Though there's usually a clear winner there, With a notable exception. That one exception is the time Canada made America cry by listing off everything he didn't like about him.
- Goes to show that even sextuplets can engage in it. The Matsuno brothers from Osomatsu-kun frequently finish each other's sentences, squabble, and confuse each other whenever more than one of them is on screen. What makes it even worse is that half the time they don't know who they're picking a fight with since they all look so similar.
- Laila and Leili of A Bride's Story. Their banter is frequently so in synch that it serves as a genuine shock to them when they have a differing opinion.
- In The Bridge of San Luis Rey, Esteban and Manuel wind up developing their own language, one that doesn't even resemble Spanish. They are too embarassed to cooperate when a priest tries to quiz them on their language.
- Robert A. Heinlein: Subverted in Time for the Stars. Tom and Pat Bartlett think they have a private language that no one else understands, which they refer to as a "prison-yard whisper". They participate in a study of twin communication, which proves that they can't understand audio recordings of the "whisper". It turns out that they're telepathic. And the telepathy is instantaneous and has no range limit. It works over interstellar distances.
- Fred and George Weasley from Harry Potter. They both can finish each other's sentences, which often includes sarcastic quips. Their Establishing Character Moment features them going back and forth, claiming their mother mixed them up again and causing their mother to do just that.
- Lori's sons Will and Rob Willis (of the Aunt Dimity series) will bicker a fair amount, sometimes with just a simple one-upmanship, sometimes in a larger succession. Their request to visit Skeaping Manor's museum prompts this exchange:
Lori: Yes, we'll go. If—
Will: We clear the table.
Rob: And load the dishwasher.
Will: And play nicely until bedtime.
Rob: And go to bed without arguing.
Will: And promise to behave ourselves in the car.
Lori (laughing): How quickly they learn.
- The Night's Blade has twin spymasters Emalley and Edwyn, and their 'creepy little double act'.
- Gem and Gemma from Power Rangers RPM are an extreme case, as it is exceedingly rare for them to individually speak in complete sentences- usually they alternate words or phrases.
- Emily and Katie of Skins were identical twins who were very different in personality, but they had a "twin language" of their own, which was subtitled in the episode where it was used:
Katie: Sham. [Sorry.]
Katie: Katie sham. [I'm sorry.]
Emily: Why are you talking Twin? We don't do that anymore.
Katie: Emsy sham doo. [Say you're sorry too.]
Emily: Emsy sham. [Sorry.]
- The Lutece twins in Bioshock Infinite. Played with in that they're not so much twins as they are gender-swapped alternate-reality versions of the same person, so it makes sense they can play off each other very well.
- The Frye twins of Assassin's Creed: Syndicate. They bicker and trade witty quips, playing off each other's personalities and knowing just what to say to push the other's buttons.
- Duumvirate: Dumumvirate bicker duo-style, without sentence-finishing.
- Jeremy and Ian from Barbie & The Diamond Castle. They even banter in song.
- The Tibble Twins on Arthur do this often, competing with each other and often getting into fights.
- Frank and Len from Ruby Gloom.