Radu leaves his dagger in the portrait of Ma, where the Prince finds it. Then, when Radu comes to kill Ma, he has the dagger again.
Radu swears by "Osiris, the high priestess". Osiris is not a priestess, on top of that it is a male name. Osiris is the god of fertility, agriculture, the afterlife, the dead, resurrection, life, and vegetation in ancient Egyptian religion.
When Hohenfels finds the dagger in the painting, he says: "This is the dagger of my servant Ragu." The word 'dagger' is misspelled as 'daggar'.
When Radu breaks through the window, a man in a white suit sitting cross-legged in a chair is reflected in the lower left-hand pane.