The Bastianelli Spike, or why this corn-ear denarius is really special

I'm just trying to identify the "spike", and learn something new; apologies for my ignorance. Could you please point out where the spike is

 

Log in or Sign up to hide this ad.

Not a problem at all. The spike is on the back of the helmet. While many dioscuri denarii feature small tufts, the signature of this series is this big single spike on the back that appears on all denominations and coins with the mintmark on the reverse(like the denarius below) and without, like my new sestertius

 

..i'm now looking at my Dioscuri coin again....i see mine has the 'mini many spikes correct?...