You will not be able to choose between the two urns by clicking on the urn pictures.
Rather, you will have to choose between the urns by clicking on a button next to which it is either written "Left Urn"
or "Right Urn".
Please be careful because the order of those buttons can change. In other words, sometimes the option
"Left Urn" might appear as the button on top and the option "Right Urn" on the bottom. But sometimes it might
be the other way around.