It wasn't very convincing.

[frindle2]

Hello. Would you please tell me what "convincing" mean in the context below?
Crenshaw growled at Aretha, but it's not for sure?
Thank you.

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from Crenshaw by Katherine Applegate
(Crenshaw is an imaginary cat of the writer, Jackson. Aretha is a pet dog. Aretha likes Crenshaw, but Crenshaw doesn't like dogs.
Jackson is afraid he is going crazy because he thinks he grow out of an imaginary friend.)

As soon as her bedroom door closed, we retreated to my room.
Crenshaw leaped onto my mattress as if he owned it.
When Aretha tried to join him, he growled. It wasn't very convincing.
"I need to understand what's happening. Am I going crazy?"

 

[MikeNewYork]

The real dog "growled" at an imaginary cat. It evidently was not much of a growl. Unless the dog is also going crazy, his noise was something else.

 

[frindle2]

Thank you for your kind reply. But I think the animal who growled was not the dog but the cat.