Double-slit experiments have been done to death, Obtaining and preserving which-path information (or otherwise) for a particle or photon causes its entangled partner to show the probability distribution with or without the interference pattern, violating Bell's inequality and thus proving nonlocality from our understanding of time and space, albeit without violating causality. Kim-et-al's delayed choice experiment brought something new to the table, whereby preserving or obscuring which-path-information for photon B caused its entangled photon A to fall in a probability distribution which showed correlation in a similar fashion, even though photon A had *already had its position recorded*. From our notion of time and space this seems to suggest not only nonlocality, but retrocausality. But an explanation that seems to make sense is that since the photon is traveling at c , thus exists as a line in spacetime instantaneously joining its creation and destruction. i.e. in the photon's frame of reference there is no time. (infinite time dilation). There are a number of quantum eraser experiments for massive particles which show post-slit collapse of the wavefunction, but I'm curious to know if there have been any experiments similar to Kim-et-al, whereby one partner is recorded before the quantum erasure is decided, using entangled massive particles travelling at a mere fraction of c? If this too displayed seeming retrocausality it would be much more spooky as it then couldn't be explained by the infinite time dilation as in the photon experiments.