could sniff
Regular verb: sniff - sniffed- sniffed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could sniff
you could sniff
he could sniff
we could sniff
you could sniff
they could sniff 	I could be sniffing
you could be sniffing
he could be sniffing
we could be sniffing
you could be sniffing
they could be sniffing	I could have sniffed
you could have sniffed
he could have sniffed
we could have sniffed
you could have sniffed
they could have sniffed	I could have been sniffing
you could have been sniffing
he could have been sniffing
we could have been sniffing
you could have been sniffing
they could have been sniffing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't sniff
you couldn't sniff
he couldn't sniff
we couldn't sniff
you couldn't sniff
they couldn't sniff 	I couldn't be sniffing
you couldn't be sniffing
he couldn't be sniffing
we couldn't be sniffing
you couldn't be sniffing
they couldn't be sniffing	I couldn't have sniffed
you couldn't have sniffed
he couldn't have sniffed
we couldn't have sniffed
you couldn't have sniffed
they couldn't have sniffed	I couldn't have been sniffing
you couldn't have been sniffing
he couldn't have been sniffing
we couldn't have been sniffing
you couldn't have been sniffing
they couldn't have been sniffing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I sniff?
could you sniff?
could he sniff?
could we sniff?
could you sniff?
could they sniff? 	could I be sniffing?
could you be sniffing?
could he be sniffing?
could we be sniffing?
could you be sniffing?
could they be sniffing? 	could I have sniffed?
could you have sniffed?
could he have sniffed?
could we have sniffed?
could you have sniffed?
could they have sniffed? 	could I have been sniffing?
could you have been sniffing?
could he have been sniffing?
could we have been sniffing?
could you have been sniffing?
could they have been sniffing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I sniff?
couldn't you sniff?
couldn't he sniff?
couldn't we sniff?
couldn't you sniff?
couldn't they sniff? 	couldn't I be sniffing?
couldn't you be sniffing?
couldn't he be sniffing?
couldn't we be sniffing?
couldn't you be sniffing?
couldn't they be sniffing? 	couldn't I have sniffed?
couldn't you have sniffed?
couldn't he have sniffed?
couldn't we have sniffed?
couldn't you have sniffed?
couldn't they have sniffed? 	couldn't I have been sniffing?
couldn't you have been sniffing?
couldn't he have been sniffing?
couldn't we have been sniffing?
couldn't you have been sniffing?
couldn't they have been sniffing?