An exclamation of satisfaction with one's self for having caught something just dropped.
Though ninjas obviously never drop anything, this is how they would drop things (and what they would proclaim) if they were capable of doing so.
The feelings of alertness and dexterity associated with the drop/catch action preceding the "Ninja Drop!" stand
in stark contrast to the inattention and clumsiness that led to the exclamation in the first place.

Anatidaephobia is defined as a pervasive, irrational fear that one is being watched by a duck. The anatidaephobic individual fears that no matter where they are or what they are doing, a duck watches.

Anatidaephobia is derived from the Greek word "anatidae", meaning ducks, geese or swans and "phobos" meaning fear.

Making a delivery without alerting the homeowner to your presence.