This paper https://physics.aps.org/featured-article-pdf/10.1103/PhysRevLett.111.240402 was discussed briefly in another thread on Klyshko photons. I have a couple of questions to anyone who has studied the work. The authors themselves note that "...even Maxwell’s equations for the classical electromagnetic field should explain the observed phenomena. Indeed, the Two State Vector Formalism adds no new predictions beyond standard quantum mechanics". Yet they describe some aspects of the experiment as "surprising". It's easy to explain the important qualitative features of all the experimental setups by applying a bit of ray tracing, some approximate "integration by eye" and some arithmetic. Based on this, my questions are:  The same ray tracing that predicts the experimental results, tells you that photons are passing through the inner interferometer all the time. They are interacting with all the mirrors all the time. Yet the authors say, "Some of [the photons] have been inside the nested interferometer (otherwise they could not have known thefrequencies fA, fB), but they never entered and never left the nested interferometer". This is not very clear.  They say, The ray tracing exercise explains this in a non-surprising way, without implying that the photons do not interact with E and F. Why do the authors conclude that the phtons interact with A and B but not with E and F?