you have defeated a flameskull

you decided to loot it's "body"? it's just a skull what did you expect to find

you pick up the skull it reignites but though warm it doesn't burn you, the skull once more laughs in an insane manner (giggles, chuckles, hideous shreiking laughter, it's the Dm's choice) the dm may also choose to have the skull mock you, but it's next to impossible that it will properly converse with you, let alone be of aid

if you try to throw the skull or rid yourself of the skull in any way it returns to float somewhere near you, you've basically been cursed to be annoyed by the skull

prolonged exposure may cause madness, use wisdom modifer to check periodically (especially if the dm decides that the skull doesn't shut up) those around you should also check 

either get creative or somebody has to roll a 25 on a charisma check to convince the skull to stop cursing you (so basically roll a nat20 and have +5 or better for the charisma modifier, good luck)

Notes: Disadvantage: Stealth, Disadvantage: Charisma Ability Checks, Disadvantage: Deception, Disadvantage: Intimidation, Disadvantage: Investigation, Disadvantage: Perception, Disadvantage: Performance, Disadvantage: Persuasion