The giant had a bonny daughter, and she and the lad grew very fond of each other. The giant said one day to Nix Nought Nothing: 'I've work for you tomorrow. There is a stable seven miles long and seven miles broad, and it has not been cleaned for seven years, and you must clean it tomorrow, or I will have you for my supper.'
The giant's daughter went out next morning with the lad's breakfast, and found him in a terrible state, for always as he cleaned out a bit, it just fell in again.
This is from " Nix Nought Nothing" in English fairly tales. I couldn't understand this sentence of "it just fell in again". Could you teach me the meaning?