How big is the Molly?
Any fish between 1" and 4" i really advise slamming hard on a hard floor, i use my bathroom floor which is concrete (really hard slam), other options for below 1" and above 4" for me, but wont go into it now.
peeps gonna get excited perhaps now and come after me, but for me, the BEST way to put a fish down is the QUICKEST way,
No disrespect Wilder, 20 seconds is a bit too long for me,
This is a tricky subject so many different views, i feel much more uncomfortable watching a fish for 20 secs in Ice than i would netting it, putting it in my hand and slamming it down hard, but thats me.....
done it a few times when needed, never seen a fish's gills move or any signs of life or movement once they hit the floor, and i always check, just to satisfy myself, i watch the fish for about 1-2 mins, then wrap up in paper and dispose. I can here peeps think "they might start moving after 2 mins or 3 mins" well i done my fair share fo checking fish on and off for up to 20 mins, never had a sign of life after a good slam
i dont expect you to go and do this now, but also, a lot of the time its not a quesiton of the fish's suffering but more what the owner is comfortable doing, atleast you honest and say you might not be able to face certain methods of killing, fair play.
However, some peeps hide behind the "i couldnt bash my fish its so barbaric" when really they saying "its makes
me feel uncomfortable" i can respect that, but they should call it how it is, THEIR discomfort.
Best Wishes, you obviously care or you wouldnt be asking
EDIT: wanted to end on a positive note
/homepage.ntlworld.com/faustus/nicol.../euthanasia.htm
LOL, good story and it makes the point well!!! 
