hissing is OK, unless they start to fight.
1	hissing	hissing	NOUN	NN	Number=Sing	3	nsubj	3:nsubj	_
2	is	be	AUX	VBZ	Mood=Ind|Number=Sing|Person=3|Tense=Pres|VerbForm=Fin	3	cop	3:cop	_
3	OK	ok	ADJ	JJ	Degree=Pos	0	root	0:root	SpaceAfter=No
4	,	,	PUNCT	,	_	3	punct	3:punct	_
5	unless	unless	SCONJ	IN	_	7	mark	7:mark	_
6	they	they	PRON	PRP	Case=Nom|Number=Plur|Person=3|PronType=Prs	7	nsubj	7:nsubj|9:nsubj:xsubj	_
7	start	start	VERB	VBP	Mood=Ind|Number=Plur|Person=3|Tense=Pres|VerbForm=Fin	3	advcl	3:advcl:unless	_
8	to	to	PART	TO	_	9	mark	9:mark	_
9	fight	fight	VERB	VB	VerbForm=Inf	7	xcomp	7:xcomp	SpaceAfter=No
10	.	.	PUNCT	.	_	3	punct	3:punct	_
