Eucalyptus leaf
A eucalyptus leaf is a vegan food item. Eating it will cure sickness and nausea if not cursed.[1] It can also be applied to use it as a whistle, acting as a magic whistle if blessed and a tin whistle otherwise. There is a 2% chance that a blessed eucalyptus leaf will become uncursed after being used as a whistle.[2]
It is fairly rare - only 0.3% of all food items are eucalyptus leaves. There is a 4.7% chance of some in Sokoban, and roughly 30.6% chance of obtaining any by kicking both trees in the forest mine town. Relevant to pacifists, it cannot be generated in any monster's inventory, as opposed to death drops.
Trivia
The effect of acting as a magic whistle seems to be based on the 1960's Australian TV show Skippy the Bush Kangaroo[3], which had a recognisable theme call that was played on a eucalyptus leaf. The show's eponymous macropod would then come bounding through the bush to whomever played the eucalyptus leaf.