Board Thread:Speculation House/@comment-27404492-20170918133425/@comment-25936766-20170926131835

SpiritedDreaming wrote:

As for why it hurt Cinder; she is the host for the Grimm. Her human nature provides a shield for it, allowing it to survive the blast. But just like an armouring shield gets damaged when struck with a sword, Cinder’s body got damaged shielding the Grimm beetle from Ruby’s Silver Eyes. Another possibility - which, admittedly, is still along those lines - is that the blast didn't do anything to Cinder since she's human, but it did cause a good deal of damage to the Grimm - who likely avoided death by virtue of the blast not being able to hit it directly.

Due to Cinder being connected to said Grimm, when the Grimm was damaged, this damage was reflected on Cinder.

In summary: Eyes don't hurt Cinder. Eyes hurt Beetlejuice. Beetlejuice is in Cinder. By hurting Beetlejuice, you hurt Cinder.