I found this example and it confuses me.

I already read about the Non-Restrictive and Restrictive Clauses and I understood the difference between them.

As I understood, I understood that the non-restrictive clause is the clause that gives extra information about a known noun in the clause and it is seperated by commas. For example:

John, who is 40 years old, is my friend.

Is a non-restrictive because the noun is already known and has been given a name "John".


A man who is 40 years old is my friend.

Is a restrictive clause because the noun is still unknown and it is just any man but his name is unknown in the clause, so its not seperated by commas.

And look at this example, please.

- I like to keep a bottle of stimulant handy in case I see a snake, which I also keep handy.

Why is this a non-restrictive?

Isn't the noun here unknown? It's " a snake" any snake but what snake it is? so shouldn't it be restrictive?
If someone keeps a snake handy, then that means he must keep it in his pocket. So this would be his pet, and the clause is non-restrictive. This sentence can only be non-restrictive. The sentence makes no sense without the comma.
He keeps the brandy in case he sees any snake, so the information is complete without the additional clause. (Incidentally, he does not keep 'any snake' handy; he keeps only a representative specimen.)