Si (pronounced 'see') is also an artifact item in the roguelike game ADOM. Probably one of the first artifacts the player is likely to see, the Si can be found somewhere in the upper levels of the Caverns of Chaos cave complex, usually at dungeon level 8 or earlier. You will know you have found the right level when you get the message "The air of this level is filled with a strange smell" upon descending the stairs. The Si is always lying on top of a trap, so you might want to give it a kick before picking it up.

As an artifact, the Si is of course indestructible. Apart from that, it may look like another useless piece of junk: you can't eat it, it's not really a weapon (although you can wield it and cause some small damage), you can't even tell what the damn thing is. Don't throw it away though, because looks can be deceiving. There's more to this nifty little accessory than meets the eye. To elaborate:

Si is an artifact that replicates.

That is to say, after a while you'll notice that your backpack has suddenly got rather heavy... it's full of sis! Enterprising souls might have guessed already that this unique capability makes them very valuable indeed. You can sell them to shopkeepers (the price goes up if they're blessed), sacrifice them to gods, even throw them around in mindless abandon. They never break, corrode or disappear into little holes on the ground. They're eternal, and they just keep on breeding like bunnies whilst lying in our backpack.

Si has certain drawbacks though. For one thing, the demented ratling won't accept it as part of his quest. More importantly, you can't drop them while exploring the Infinite Dungeon - like faithful puppies, they keep on re-emerging in your backpack whenever you go down the stairs. Sooner or later, their weight will become too much, so drop your sis before entering IF.