Current cosmological data provide convincing evidence that the correlations observed in the CMB sky can be traced back to the state of quantum fields at the beginning of inflation. This state is highly entangled, it has correlations at space-like separations. In this talk I discuss a candidate origin of such correlations, the production of entanglement in a BKL phase of the pre-inflationary universe, and describe possible imprints in the CMB sky.