Please note that "Chalitzah" refers to the rite which frees a man and woman from their obligation to perform levirate marriage.
Whether this is necessary: Yevamot 104a-b
Requirement for the Judges to See the Saliva: Yevamot 101b, 106b
Must be in front of the Brother-in-Law: Yevamot 106b
If the woman Spits Without Intent: Yevamot 102b, 104b
If She Spat Blood: Yevamot 105a
If the Saliva was borne away by the Wind: Yevamot 106b
If She didn't actively generate the Saliva, but rather it was induced by an exterior force: Yevamot 106b
Whether this Must be after shoe-removal, and if it wasn't: Yevamot 105a