When they are just jumping at each other and their tails are wagging that means that they are playing.
1	When	when	ADV	WRB	PronType=Int	5	advmod	5:advmod	_
2	they	they	PRON	PRP	Case=Nom|Number=Plur|Person=3|PronType=Prs	5	nsubj	5:nsubj	_
3	are	be	AUX	VBP	Mood=Ind|Number=Plur|Person=3|Tense=Pres|VerbForm=Fin	5	aux	5:aux	_
4	just	just	ADV	RB	_	5	advmod	5:advmod	_
5	jumping	jump	VERB	VBG	Tense=Pres|VerbForm=Part	15	advcl	15:advcl:when	_
6	at	at	ADP	IN	_	7	case	7:case	_
7	each	each	DET	DT	ExtPos=PRON|PronType=Rcp	5	obl	5:obl:at	_
8	other	other	ADJ	JJ	Degree=Pos	7	fixed	7:fixed	_
9	and	and	CCONJ	CC	_	13	cc	13:cc	_
10	their	their	PRON	PRP$	Case=Gen|Number=Plur|Person=3|Poss=Yes|PronType=Prs	11	nmod:poss	11:nmod:poss	_
11	tails	tail	NOUN	NNS	Number=Plur	13	nsubj	13:nsubj	_
12	are	be	AUX	VBP	Mood=Ind|Number=Plur|Person=3|Tense=Pres|VerbForm=Fin	13	aux	13:aux	_
13	wagging	wag	VERB	VBG	Tense=Pres|VerbForm=Part	5	conj	5:conj:and|15:advcl:when	_
14	that	that	PRON	DT	Number=Sing|PronType=Dem	15	nsubj	15:nsubj	_
15	means	mean	VERB	VBZ	Mood=Ind|Number=Sing|Person=3|Tense=Pres|VerbForm=Fin	0	root	0:root	_
16	that	that	SCONJ	IN	_	19	mark	19:mark	_
17	they	they	PRON	PRP	Case=Nom|Number=Plur|Person=3|PronType=Prs	19	nsubj	19:nsubj	_
18	are	be	AUX	VBP	Mood=Ind|Number=Plur|Person=3|Tense=Pres|VerbForm=Fin	19	aux	19:aux	_
19	playing	play	VERB	VBG	Tense=Pres|VerbForm=Part	15	ccomp	15:ccomp	SpaceAfter=No
20	.	.	PUNCT	.	_	15	punct	15:punct	_
