1.   There would be blue sparks flying.

2.   There was a pop, and a fat blue spark.

3.   Blue sparks and flashes were streaking from one of the engines.

4.   Large blue sparks flashing around the motor commutator indicate worn brushes.

5.   The subway racketed overhead, emitting blue sparks.

6.   Police were seen charging the crowd of several thousand using batons and shields that give off blue sparks and electric shocks.