Non-Gaussian quantum states, whose Wigner functions can take negative values, are important both for fundamental tests of quantum physics and for quantum information technologies that have been actively developing during the last decades. A typical example of a non-Gaussian state is the so-called Schrödinger's cat state. Its very interesting feature is that its "classical" part (two Gaussian maxima) is spatially separated from the "non-classical" one (the interference strips). In this paper we consider several methodological issues related to these strips.