Serbians etc. sound to Bulgarians like they aren't sure what happened.

I like this:

Tense system also isn't that big of a deal. The only think I can think is that when listening to other Slavic languages, including Serbian, their past simple tense is the same as our past renarrative mood which we use for things we did not witness or are not sure happened. So when I listen to Serbian, it always sounds like they aren't sure about what happened.