Multum In Parvo is Latin for "much from little" because that's exactly what you make happen!
The effect is simplicity itself: show four clear transparent tumblers- a small, a medium, a large and a jumbo tumbler. Each tumbler is TWICE the size of the one before it. Now fill the smallest tumbler to the brim with milk. Pour the milk from the small tumbler into the medium tumbler. It should fill the medium tumbler halfway, right? NO- the milk keeps pouring out of the small tumbler filling the medium tumbler to the brim! Impossible!
But wait- there's more! Pour the milk from the medium tumbler into the large tumbler- again, the milk keeps pouring until the large tumbler is filled to the brim!
There's more! Pour the milk from the large tumbler into the jumbo tumbler- yes, the jumbo tumbler gets filled to the brim! Remember, this is the same milk that started out just filling the small tumbler, and now the jumbo tumbler is filled!
And there's still more! You can now reverse the effect, pouring down into smaller and smaller tumblers!
Performance Ideas
You may use any kind of liquid in the tumblers, especially liquid colored with food coloring so that it shows up (plain water is clear- it won't show up).
If you want the look of milk, you probably do not want to use regular cow's milk with this routine, as milk can spoil, and because of the fat content can be difficult to rinse out of the tumblers.
Option 1: use soy milk, which does not spoil and can be sipped during the routine to prove that it's real milk.
Option 2: mix up some powdered milk just before showtime. Again, the milk can be sipped, and it is easy to transport because you keep it in powdered form until you use it.
Option 3: NOT RECOMMENDED to use the solution marketed as OOM. This is concentrated machinist's cutting oil which, when mixed with water, turns the water a milky color. It's not suitable to be ingested! It also has a strong smell; your audience will know it's not real milk, and will mistakenly think that the trick works by using some sort of fake milk. Plus the oil will cause your tumblers to discolor over time. Not good!