In some families, twins speak to each other in a language that only they can understand. Scientists even came up with a name for such a phenomenon: “cryptophasia” (from the Greek kryptos and phasis – “hidden speech”).
Toddlers repeat facial expressions and gestures of each other. Sometimes twins communicate in their own language for up to three years, then they switch to the generally accepted language of the environment.
The twins’ conversation is in the video below.