I'm assuming it's to scare off predators / like how they will puff up their neck spikes to make them look bigger to predators or enemies.
1-2	I'm	_	_	_	_	_	_	_	_
1	I	I	PRON	PRP	Case=Nom|Number=Sing|Person=1|PronType=Prs	3	nsubj	3:nsubj	_
2	'm	be	AUX	VBP	Mood=Ind|Number=Sing|Person=1|Tense=Pres|VerbForm=Fin	3	aux	3:aux	_
3	assuming	assume	VERB	VBG	Tense=Pres|VerbForm=Part	0	root	0:root	_
4-5	it's	_	_	_	_	_	_	_	_
4	it	it	PRON	PRP	Case=Nom|Gender=Neut|Number=Sing|Person=3|PronType=Prs	7	nsubj:outer	7:nsubj:outer	_
5	's	be	AUX	VBZ	Mood=Ind|Number=Sing|Person=3|Tense=Pres|VerbForm=Fin	7	cop	7:cop	_
6	to	to	PART	TO	_	7	mark	7:mark	_
7	scare	scare	VERB	VB	VerbForm=Inf	3	ccomp	3:ccomp	_
8	off	off	ADP	RP	_	7	compound:prt	7:compound:prt	_
9	predators	predator	NOUN	NNS	Number=Plur	7	obj	7:obj	_
10	/	/	PUNCT	,	_	7	punct	7:punct	_
11	like	like	SCONJ	IN	_	15	mark	15:mark	_
12	how	how	ADV	WRB	PronType=Int	15	advmod	15:advmod	_
13	they	they	PRON	PRP	Case=Nom|Number=Plur|Person=3|PronType=Prs	15	nsubj	15:nsubj	_
14	will	will	AUX	MD	VerbForm=Fin	15	aux	15:aux	_
15	puff	puff	VERB	VB	VerbForm=Inf	7	advcl	7:advcl:like	_
16	up	up	ADP	RP	_	15	compound:prt	15:compound:prt	_
17	their	their	PRON	PRP$	Case=Gen|Number=Plur|Person=3|Poss=Yes|PronType=Prs	19	nmod:poss	19:nmod:poss	_
18	neck	neck	NOUN	NN	Number=Sing	19	compound	19:compound	_
19	spikes	spike	NOUN	NNS	Number=Plur	15	obj	15:obj	_
20	to	to	PART	TO	_	21	mark	21:mark	_
21	make	make	VERB	VB	VerbForm=Inf	15	advcl	15:advcl:to	_
22	them	they	PRON	PRP	Case=Acc|Number=Plur|Person=3|PronType=Prs	21	obj	21:obj|23:nsubj:xsubj|24:nsubj:xsubj	_
23	look	look	VERB	VB	VerbForm=Inf	21	xcomp	21:xcomp	_
24	bigger	big	ADJ	JJR	Degree=Cmp	23	xcomp	23:xcomp	_
25	to	to	ADP	IN	_	26	case	26:case	_
26	predators	predator	NOUN	NNS	Number=Plur	23	obl	23:obl:to	_
27	or	or	CCONJ	CC	_	28	cc	28:cc	_
28	enemies	enemy	NOUN	NNS	Number=Plur	26	conj	23:obl:to|26:conj:or	SpaceAfter=No
29	.	.	PUNCT	.	_	3	punct	3:punct	_
