Snotlout and Hiccup don't talk about it.
They don't talk about the days where the migraines hit. The days where Snotlout just goes to his cousin, and curls up in pain.
They don't talk about how muffled everything is to Snotlout, or how Hiccup's stump aches more sometimes for more than just the phantom pain from the Red Death.
They don't talk about the lightning scars all over Snotlout's body. How Hiccup has faint ones that are harder to see.
The way Snotlout rubs his hands sometimes when they ache, especially where the small lightning scars on them are.
The first time Eret really notices it, it's because Astrid sighs, and says Snotlout stayed with them for the night, and I never knew it was that bad.
So he watched closer, the next time he saw Snotlout.
He saw the small frown, the focus of his line of sight being Valka's mouth, and when it's bathing day, he sees the scars on Snotlout.
He doesn't know those kinds of scars.
He asks calmly, if it was a dragon fight or something, because he learned about the fight with Krogan and Viggo and all.
Snotlout, back to him, doesn't respond.
He asks Hiccup, later, who sighs, and says they both were hit by lighting - a handful of times for Hiccup now, but far more for Snotlout, at this point. Explains he (Hiccup) has it a bit easier, but Snotlout has lasting pain, and can't hear well - that everyone thought he was being a pest on purpose, but he genuinely never heard the directions and such.
When it gets bad, I help him, since his parents don't.
"Wait, how many times has he been struck?"
"It was 12 times, back when we were fifteen, I think. Honestly, I kind of lost count by the time we were seventeen."
(He always makes to face Snotlout when talking to him, after. Snotlout is confused.)