A watcher, once discovered, could always be replaced by another.
1	A	a	DET	IND-SG	Definite=Ind|PronType=Art	2	det	_	_
2	watcher	watch	NOUN	SG-NOM	Number=Sing	10	nsubj:pass	_	SpaceAfter=No
3	,	,	PUNCT	Comma	_	5	punct	_	_
4	once	once	ADV	_	NumType=Mult	5	advmod	_	_
5	discovered	discover	VERB	PASS	Tense=Past|VerbForm=Part|Voice=Pass	10	advcl	_	SpaceAfter=No
6	,	,	PUNCT	Comma	_	5	punct	_	_
7	could	could	AUX	PAST-AUX	VerbForm=Fin	10	aux	_	_
8	always	always	ADV	_	_	10	advmod	_	_
9	be	be	AUX	INF	VerbForm=Inf	10	aux:pass	_	_
10	replaced	replace	VERB	PASS	Tense=Past|VerbForm=Part|Voice=Pass	0	root	_	_
11	by	by	ADP	_	_	12	case	_	_
12	another	another	PRON	ADJ-SG	Case=Nom	10	obl	_	SpaceAfter=No
13	.	.	PUNCT	Period	_	10	punct	_	_
