Quantum tunnelling via bubble nucleation during inflation is a quite common phenomenon in the string theory landscape. In this talk, first I discuss the evolution of fluctuations in a scalar field considering non-linear interactions during and after the bubble nucleation. Second, I give a model where a bubble of a low energy scalar field is nucleated during slow-roll inflation and affects the fluctuations of the universe. Lastly, I show that, in such a model, a bubble-shaped high skewness region may appear in observations of the temperature fluctuations of the Cosmic Microwave Background. It can be large enough to be detected in the near future, and if detected it will bring us invaluable information about the physics in the early universe.