Bones

Bones are items dropped by all players and most monsters (excluding spiders, bats, giants, dragons, and demons) upon death, which can be buried to gain Prayer experience. They are the lowest type of bones in as they only yield 3.75 experience when buried.

25 bones are required to complete the Demon Slayer quest, and 3 to open the Tomb Doors during Shilo Village.

Bones gathering
The following monsters are easy to kill and therefore are a good source of bones:
 * Chickens
 * Cows
 * Gnome troops
 * Goblins

Item spawns
There are also many bone spawns throughout Gielinor, particularly in the Wilderness and the battle field.
 * Edgeville dungeon
 * Battle field
 * West of Yanille
 * Ogre infested Ruins (3 spawns)
 * Grew's jangerberry island (2 spawns)