If it won't take pre-killed and you usually feed live then you could hold the rat by the tail and whack it against a hard surface, like a refrigerator or wall.
1	If	if	SCONJ	IN	_	5	mark	5:mark	_
2	it	it	PRON	PRP	Case=Nom|Gender=Neut|Number=Sing|Person=3|PronType=Prs	5	nsubj	5:nsubj	_
3-4	won't	_	_	_	_	_	_	_	_
3	wo	will	AUX	MD	VerbForm=Fin	5	aux	5:aux	_
4	n't	not	PART	RB	_	5	advmod	5:advmod	_
5	take	take	VERB	VB	VerbForm=Inf	15	advcl	15:advcl:if	_
6	pre-killed	pre-killed	ADJ	JJ	Degree=Pos	5	obj	5:obj	_
7	and	and	CCONJ	CC	_	10	cc	10:cc	_
8	you	you	PRON	PRP	Case=Nom|Person=2|PronType=Prs	10	nsubj	10:nsubj	_
9	usually	usually	ADV	RB	_	10	advmod	10:advmod	_
10	feed	feed	VERB	VBP	Mood=Ind|Number=Sing|Person=2|Tense=Pres|VerbForm=Fin	5	conj	5:conj:and|15:advcl:if	_
11	live	live	ADJ	JJ	Degree=Pos	10	obj	10:obj	_
12	then	then	ADV	RB	PronType=Dem	15	advmod	15:advmod	_
13	you	you	PRON	PRP	Case=Nom|Person=2|PronType=Prs	15	nsubj	15:nsubj|22:nsubj	_
14	could	could	AUX	MD	VerbForm=Fin	15	aux	15:aux	_
15	hold	hold	VERB	VB	VerbForm=Inf	0	root	0:root	_
16	the	the	DET	DT	Definite=Def|PronType=Art	17	det	17:det	_
17	rat	rat	NOUN	NN	Number=Sing	15	obj	15:obj	_
18	by	by	ADP	IN	_	20	case	20:case	_
19	the	the	DET	DT	Definite=Def|PronType=Art	20	det	20:det	_
20	tail	tail	NOUN	NN	Number=Sing	15	obl	15:obl:by	_
21	and	and	CCONJ	CC	_	22	cc	22:cc	_
22	whack	whack	VERB	VB	VerbForm=Inf	15	conj	15:conj:and	_
23	it	it	PRON	PRP	Case=Acc|Gender=Neut|Number=Sing|Person=3|PronType=Prs	22	obj	22:obj	_
24	against	against	ADP	IN	_	27	case	27:case	_
25	a	a	DET	DT	Definite=Ind|PronType=Art	27	det	27:det	_
26	hard	hard	ADJ	JJ	Degree=Pos	27	amod	27:amod	_
27	surface	surface	NOUN	NN	Number=Sing	22	obl	22:obl:against	SpaceAfter=No
28	,	,	PUNCT	,	_	22	punct	22:punct	_
29	like	like	ADP	IN	_	31	case	31:case	_
30	a	a	DET	DT	Definite=Ind|PronType=Art	31	det	31:det	_
31	refrigerator	refrigerator	NOUN	NN	Number=Sing	22	obl	22:obl:like	_
32	or	or	CCONJ	CC	_	33	cc	33:cc	_
33	wall	wall	NOUN	NN	Number=Sing	31	conj	22:obl:like|31:conj:or	SpaceAfter=No
34	.	.	PUNCT	.	_	15	punct	15:punct	_
