  An understanding of the interaction of a point charge and a magnetic moment
is crucial for understanding the experiments involving electromagnetic momentum
carried by permeable materials as well as the experimentally-observed
Aharonov-Bohm and Aharonov-Casher phase shifts. Here we present two simple
models for a magnetic moment which have vastly different interactions with a
distant point charge. It is suggested that a satisfactory theoretical
understanding of the interaction is still lacking and that the "hidden
momentum" interpretation has been introduced into the textbook literature
prematurely.
