Sometimes a map had a randomly placed event item in it which could be collected to purchase items in one of the four shops in the event map. Once collected on the maps, event items would appear on your back and wouldn't be obtained until you brought the cheese to the hole. You could spend these currencies on the event map in the shop listed below.
Five seconds had to pass before you can collect the event item on a map.
Four-Leaf Clovers were tradeable, but not Pots o' Gold and Lucky Horseshoes.
This may or may not be a bug.
As of the V1.294 update, mice will have the cheese and event items (such as the Four-Leaf Clover) equipped, if they collected said items before their death, once they are revived by a shaman using the Ambulanceskill.
The event item part of this update was likely added to the game in preparation for this event.
Mice who collected the event item, died, and then got revived will have the event item when they respawn, but it won't show on their backs.
In Mouse Transformation maps with an event item in it, transformed mice would still be shown holding the event item if they held it before transforming.
The Paintbrush item is seen as controversial by many people because of the ability to draw inappropriate things and words without the ability to hide the drawings, like you can with whispers and stationery paper.