Don't you mean a Sacrificial Alt
ar?
Anyways, here's a quick help guide:
[spoiler = "spoiler"]
http://i.imgur.com/QrxsD6s.png
This is the so called altar. To throw an item into it, be sure to keep a right distance, so that the player drops the item in front of the altar.
http://i.imgur.com/0KBR3rD.png
After standing at an acceptable distance(the player from the altar), enter your inventory and highlight the item you wish to drop. Pressing [D] after highlighting the mentioned item will make the player drop it after exiting the pause menu. In this occasion, I will be dropping one Emerald.
http://i.imgur.com/SNojnj2.png
After exiting the pause menu, the player will throw/drop the selected item, as mentioned before. After the item touches the ground, hang in there for a second, and you will get a rather pleasing surprise.
On the other hand, while I was playing version 102 (maybe this bug was fixed in version 103), I ran accross something very funny:
http://i.imgur.com/ar8d429.png
So, after killing a bat in the air, it dropped a coin just where it received it's final blow. What happened is that, instead of falling, the coin kept (slowly) moving towards the top of the screen.
http://i.imgur.com/d26q242.png
After a few seconds, the coin could not go any further, and just stopped to take a rather surprising rest.
http://i.imgur.com/l4CNQQQ.png
Aww, man. C'mon! Really?![/spoiler]
Edit: Spoilers aren't working. Why?
poe Edit: Fixed, see my post