When striking a minecart with an enchanted sword (Sharpness 5) the enchantment particles appear and the minecart is broken and player was awarded the Overkill achievement.
Comments 2
Although it used to say 8 hearts (due to a bug fixed in 14w32a), it has always been 9.
http://minecraft.gamepedia.com/Achievements#History
fixed in 1.8, but under the achievement, it says you have to deal 9 hearts of damage, and I'm not sure if they changed it, but it used to be 8 hearts.