A eucalyptus leaf is a vegan food item. Eating it will cure sickness, and it can also be applied to use it as a whistle. It will act 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.
The effect of acting as a magic whistle seems to be based on the 1960's Australian TV show Skippy the Bush Kangaroo, 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.