Final answer:
The statement implies a coming betrayal, and the literary element being used is foreshadowing.
Step-by-step explanation:
The statement implies a coming betrayal, as the author mentions that no treachery hid in the smiles of Hrothgar and Hrothulf. The literary element being used in this statement is foreshadowing. Foreshadowing is when the author provides hints about the plot developments to come before they happen.