Since the wires from the batteries and blasting cap are connected to either metal strip, when they touch, the circuit will be complete and it will detonate the explosive charge.
(the wires from the batteries and blasting cap; are connected; ) (they; touch; ) (the circuit; will be; complete; T:when they touch) (it; will detonate; the explosive charge)
the wires from the batteries and blasting cap they the circuit it
are connected touch will be will detonate
complete T:when they touch
the explosive charge