A battery is wired in such a fashion that when the the metal L is at rest, the circuit is just completed, which causes the big nail to become an electromagnet.
(A battery; is wired; ) (the the metal L; is; at rest) (the circuit; is just completed; T:when the the metal L is at rest)
A battery the the metal L the circuit
is wired is is just completed
at rest
T:when the the metal L is at rest