This experimental poetry form is called 3 3 6. The form is as follows:
The first line has three words.
The second line has three words, that are not any of the words from the first line.
The third line has all of the words from the first and second lines, but no more and not in exactly the same order as they were in the first and second lines.
Here is an example:
The still cat,
watches a dog.
A still dog watches the cat.