The Jack In The Box Phenomenon
For some reason, humans seem to love to be frightened, shocked and surprised.
Watch a young child turn the handle and hear "Round and Round The Mullberry Bush - The Monkey Chased The Weasle - The Monkey Thought It Was All In Fun . . ."
The child's first experience with this thing is shock, fright and surprise. Depending on the age of the child, some crying and screaming may be involved. Regradless of the initial reaction, the child will invariably close the lid and crank the handle again. Despite knowing, and therefore anticipating, the outcome of turning the crank, the child will still turn the crank and still be shocked - and surprised - and delighted when the lid of the box snaps open and Jack pops out and bounces around.
Another thing about humans is our curiosity. When faced with something unfamiliar, or familiar - but in some way unfamiliar - we want to answer "What" and "Why".
WHY is THAT there?
WHAT would happen if I?.
These questions are often are followed by the next obvious question -
When you see something that looks obviously like a key meant to wind something up - you're almost compelled to turn it - and wind something - which you can't see - up.
And if that key is sticking out of something very familiar, something so ubiquitous that it usually goes unnoticed, in a setting that clearly has been set up to specifically focus attention on the object - the urge to Wind That Key is almost irresistable.
Now put that key in the side of what is obviously a coffee mug - with what appears to be coffee in it - and you've got the makings of a potentially interesting, and maybe a little, surprisingly delightful, experience.
There is a possibility that whatever is being wound up will, when unwinding, cause the coffee to spill or splash out - or maybe cause the cup to tip over - or there might be a Jack In The Box inside the cup waiting to pop out and startle you . So there's an element of risk is involved. Or - it may only wind up a music box hidden inside the cup - and play a pleasant familiar tune. You just won't know until you turn that key, wind up whatever's attached to the key - and see what happens.