Sometimes when I wake up in the middle of the night, my mouth feels like a snake has slept in it and left its blanket behind. My mouth gets that uncomfortable woolly feeling that only a good cup of tea can resolve.
Now, just imagine that the cat’s got your tongue. It’s climbed into your mouth, and with its claws yanked out your tongue to ferry away and eat somewhere as a delicacy.
This creates a lively visual picture, vivid enough to have us believe that we cannot speak if the cat has our tongue.
“Cat got your tongue?” is an idiom that dates back to the 18th century and is asked of someone who is not responding. This is particularly so, for example when a child is asked, “Why have you not done your homework,” and there is silence. The adult would say, “What’s the matter, cat got your tongue?”
The most confident source on its origin comes from www.theidioms.com
“This phrase has an interesting origin. In the 18th century, the English Navy had the practice of whipping erring sailors with a whip which had multiple endings. This whip was nicknamed “the cat” because it commonly had nine endings. So, after receiving a beating, while the poor sailor lay in a corner sulking or not speaking, other sailors will walk up to him and tease, “Did the cat get your tongue?”, referring to the whip. As time went on, this became shortened to Cat got your tongue.
The expression “cat got your tongue” is always directed at someone else. You could never say in response to a question, “The cat’s got my tongue,” because by making this utterance you are making it clear that your tongue is well placed in your mouth and you are free to use it.