This episode has Matt and Rowan talking about case marking, a way to indicate what each noun is doing in the sentence. Specifically, what Matt refers to as "non-default case marking" - parts of languages where cases behave in ways that don't fit with their canonical uses in the rest of the language.

Paper mentioned: https://mitcho.com/subjex/aldridge.pdf

Many of the examples are from Ergativity by R.M.W. Dixon