[Seras manages to hold in a sigh as she tries to explain.]

I suppose I don't really need it... but it's what I'm used to, it's what vampires do. We're nocturnal by nature, we like the dark and coffins shut out the light particuarly well. My master was quite forceful about me doing so after I was first turned, it's traditional I suppose, on account of us being 'undead'.

Now I can't seem to sleep properly without one.