Zippy, it's a good thing your battery didn't have any outgassing going on, or you could have seen a big ball of fire instead of a hot spark !
that is NO place to check spark out put ! have you ever seen a battery blow up ?

PLEASE GUYS. DON'T have, or cause HOT SPARKS AROUND BATTERIES !
you were VERY LUCKY this time, but next ?

sorry for the rant, but SAFETY FIRST !

next time, use the intake manifold or head bolt the negative cable attaches to.

rant over.