"That depends," Cullen says darkly, "on what she put in it. Dorian's formed an alliance with her. He feeds her information about assorted awful things one can put in anything edible, and in return she swears not to use them on him."

Cullen isn't scared of Sera. That would be overstating it. Rather, he's... very cognizant that she shouldn't be crossed, if at all avoidable.