Two instances of dangling causes and foreshadowing occurs as Harry sees the face of Sirius Black in the crystal ball and an entranced Professor Trelawney speaks of a future event that will occur later that night.
Fifty-three years ago, Jerry's Uncle Leo stiffed Jerry's mother out of $50. Eager to get it back, Jerry's father says, "Do you know what that's worth today in interest alone? $663.45, figured at a conservative 5% interest, compounded quarterly." Morty's calculations are almost accurate, though he does not compound quarterly, and his sum includes the principle, not just the interest.