There is no Loch Ness monster but a replica was built and actually put in the lake and it may or may not be bewildering to the stupid animals when they see it motionless (but not decaying) on the lake floor.
Billy Wilder's movie isn't about that particular monster though. It does lead to a climactic reveal of a fake monster (mechanical wonder and failure) and the other characters react to the world famous Detective Holmes with a slower animal's bewilderment. The perspective is both sympathetic and cynical on the overlap of intelligence and sickness and the mournful end of a better age of men. Holmes is of an advanced mental acumen, so the terror conveyed is in being so close to a force that's always a level above and the gags unfold with the comedy of constant delay.