Meaning of sonic blank slates

[Tan Elaine]

Rabbits are sonic blank slates in contrast with a happy cat that purrs and an unhappy dog that whines.

What does the phrase mean?

Thanks.

[Tdol]

I think it means that we don't know what noise rabbits make. (I am not sure of this, though)

[susiedq]

In this sentence, a "blank slate" is used to mean the unknown or not revealed. So, because rabbits don't make noise, they don't reveal their feelings, like the cat or the dog.

It is an unusual use of this expression in that sentence.