Why a raven is like a writing desk?

It creaks, It has legs, It is black,
It eats paper, creates litter, lots of slack
frustrates you if you are a sitter
It is very very bitter
It can knock you out
lets you walk about
It is curious to the hilt
Has a very strong built
And it doesn’t wear a kilt
It is not made of plastic
Its finish is fantastic
as I make things up
drinking tea in a cup
with my friend mad hatter
whose question is the matter
he seems quite pleased
riddle’s answer finally released
Raven suddenly flies far
contemplation left ajar