Hissing isnt a great sign. As far as I know, snakes do this when scared. You do not want to scare the snake with a food item as this can condition them to not take the item at all. You are supposed to dangle lightly, and if it doesnt take you can lie it with them for 30-40 mins (or overnight if you wish--> if its in the tank). If the food item is not eaten, try again on your next regular feeding.