The Bones to Bananas spell can be used to turn all bones in one's inventory to bananas. It requires two water runes, two earth runes, and one Nature rune to be cast, with a Magic level of 15. This spell is very useful when fighting monsters which drop bones as a 100% drop, as the bananas produced heal 2 hitpoints each.
If you are casting the spell only for Magic exp, add only one bone to your inventory at a time as it turns ALL bones in inventory into bananas for only 25 exp per spell regardless of number of bones. At least one bone or big bone must be in your inventory to be able to cast the spell.