This video shows a toggle flip flop made from copper contact relays. Initially there was a problem with oscillation of the relay contacts after the relay opens: because the contact separation distance is less than the nail-nail distance, it is possible for the contacts to re-contact after opening as the nail vibrates briefly after the contact opens. Only the DPST relay exhibited this problem, and it was solved by bending a piece of insulated wire in such a way that after opening, a contact hits the wire, damping the oscillation enough to prevent the problem.

Here is a close-up photo of two of the relays (before the damping solution had been implemented for the DPST relay):