Comics lettering is a discipline all its own that I'm trying to learn alongside everything else! 😆 Interestingly it’s evolved its own rules and visual "language." Em dashes are occasionally used in comics from the U.K. but aren't used in American comics. Good eye for detail though, as you made me think about it and I may change this to an ellipses. The double hyphen is used in place of semi colons or as a representation of a character getting interrupted. Ellipses are used to represent a character's speech fading in and out due to something like this case of injury/delirium. It's a tough call as I think of it as the character making a deliberate pause as he ascertains what he sees (double hyphen) but he's definitely addled as well making a case for (...) 🤔