Slut! Neville/FILK question

[Martha]

Jeff:

<except that poor Neville hardly gets to sleep with anybody>

bboy_mn:

<From my experience.... ah... as a reader... that is... Neville has 
one redeeming quality, and that is, he is quite 
large ...ah... ...nudge,
nudge, wink, wink, ...if you know what I mean.>

And finally Martha:

This reminds me of a fanfic I read ages ago (and therefore cannot 
remember where I found it or who it's by). Anyway, it features the 
Gryffindor boys playing a game I am reliably informed is known 
as "soggy biscuit" or alternatively "ooky cookie". To avoid offending 
anyone I won't describe it explicitly - but let's just say it 
involves the depositing of a particular male bodily fluid on to a 
particular snack item. The last participant to do so is given the 
forfeit of eating it. Anyway, in the fic, as I remember it, Harry is 
the first to - er - well, you know, and Neville is the last. So yeah, 
Neville lasts longest. Another redeeming quality, non? Even if he has 
eaten a biscuit with THAT on it.

Enough of this, before it gets overly icky, and a question or two 
about filks:

1) Do filks have to be set out like songs in a musical - you know, in 
context and everything - or can I just write a song so it's about 
something or someone, not meant for any specific character to sing?

2) Do filks have to be based on rock-solid canon? (I have had an idea 
you see, but it's certainly not canonical and I don't want to write 
it unless I'm sure it's OK. It'll be about Slashfic-Sirius - the one 
who is still at school and particularly promiscuous).

If anyone knows the answers I'd be ever so grateful to hear them.

~ Martha (wearing her glittery "siriusSLASHremus" t-shirt, 
incidentally)