Or if he makes a request for a fish, will give him a snake?

For as Jonah was three days and three nights in the stomach of the great fish, so will the Son of man be three days and three nights in the heart of the earth.

Again, the kingdom of heaven is like a net, which was put into the sea and took in every sort of fish:

But, so that we may not be a cause of trouble to them, go to the sea, and let down a hook, and take the first fish which comes up; and in his mouth you will see a bit of money: take that, and give it to them for me and you.