Learn German: Dank des Geldes sitzt er am Tisch, die Arme verschränkt. - Thanks to the money, he sits at the table, arms crossed.

This is the absolute accusative structure you are currently learning. It pairs a noun in the accusative case (die Arme) directly with a participle or adjective (verschränkt) to describe a posture or accompanying circumstance. It translates naturally to "with his arms crossed" in English, but German drops the "with" and relies on the case structure instead.

Since die Arme looks the same in both nominative and accusative, how do we know it is accusative here?

The absolute accusative construction strictly requires the accusative case by definition. While feminine and neuter nouns (and plurals like die Arme) look identical in nominative and accusative, a masculine noun would show it clearly. For example, if he sat "with his head lowered," it would be den Kopf gesenkt, showing the unmistakable masculine accusative den.

Why does verschränkt come after die Arme rather than before it?

In an absolute accusative phrase, the participle expresses the current state or action of the noun. If you put it before the noun (die verschränkten Arme), it becomes a normal adjective meaning "the crossed arms." Placing it after the noun creates the independent meaning "his arms [being] crossed."

I thought the preposition dank took the dative case. Why is it dank des Geldes here?