If only one shoe of a train car is on the third rail, what can be said about the other shoes?

When a train car has only one shoe in contact with the third rail, the other shoe is effectively not receiving any electrical current. The third rail is designed to power the train, and each shoe is meant to connect to it to draw electricity. If one shoe is on the third rail, the other shoe that is not making contact is inactive because it cannot draw power.

The correct understanding is rooted in the functioning principle of the third rail system. The shoes are designed to collect electricity from the rail to power the train's motors. If one shoe is engaged and the other is not, the shoe that is not in contact does not function, making it inactive in the sense that it does not play a part in current collection at that moment. Therefore, the other shoe is not ‘alive’ in terms of electrical function and does not sustain any damage merely by being out of contact. It simply cannot contribute to the operation of the train while it is not engaged with the rail.