system
Given the following post, respond as if you're commenting on Reddit:
human
[Discworld]About the Luggage.

I know it's made from sentient/sapient pearwood, but why does it have teeth and a tongue? Also, where do it's legs come from? And why does it have a gender? One would imagine it was just a lump of wood magically brought to some odd kind of a life... It has made children with a female Luggage, so it clearly has a gender and some kind of reproductive organs (i don't want to know)

I haven't seen these questions answered in the books (granted, i haven't read quite all of them, i haven't read Raising Steam, some of the Tiffany books, and i haven't had a chance to read the supplementary science of Discworld books), so if they are, i'm sorry.
gpt
*Cracks her knuckles*

Right, I've been reading these books obsessively for the last 10 years. Here's where it pays off.

*Ahem*. 

The Luggage is the magical result of a large wooden chest made out of sapient pearwood. This is the most intelligent, malevolent tree on the Disc, and will only grow in areas of dangerously high raw magic such as the sites of magical battles during the time of the Dark Emperor (who was a sourcerer and therefore a source of raw magic).

The Luggage is, as a result, a multidimensional middle-finger to the entirety of logic and reason. It's produced from a substance that's so far down the end of the probability curve it's approaching normality from the other side, and as a practical upshot of this it's also massively influenced by belief. For example, Rincewind is always faintly suspicious that it can stare you down when it doesn't have eyes. However, the fact that he believes it can means that it will, in the future, continue to be able to do so.

People believe that something so ridiculously and almost cartoonishly malevolent as the Luggage needs to have big, tombstone teeth and a mahogany tongue, and therefore it will do. 

Plus, as Ponder Stibbons likes to explain to Archchancellor Ridcully when he doesn't really want to have to explain how reading invisible writings works or similar... "it's all done by magic Archchancellor".