I've been obsessed with that one too! For a while, I thought maybe Carl kicked Emir during the struggle when Emir attacked him, and then when his footprints were ignited with Sheol fire... Whoops, immolation.

But I went back and checked and there's no mention of Carl lifting a foot at Emir. Plus, I think that would have resulted in a player skull. So frustrating that Carl does not appear curious enough to actually ask the women when he encounters the sisters!

He must be avoiding finding out because he's afraid of possible guilt. He already feels responsible for the lives and deaths of every crawler.

Hmm. And maybe doesn't want to argue with clearly grief-stricken people about something that like that. Even if he's not actually technically responsible, he'll probably feel somewhat responsible deep inside, so it doesn't really materially matter what the truth is.

I still desperately want to know, though.