the incomprehensible muttering

On days like that he would stand up. Then he would just stand there, without moving. He would clench his fists tight and his face would suddenly turn purple (...) and the incomprehensible muttering. He'd begin by pacing, circling the table. Not the pacing of somebody killing time or thinking something over, but the pacing of a man who doesn't know what to do with his anger. 

- The End of Eddy, Eduard Louis (2014)