Why does The Cowboy say MOO?

Well I am not for sure the answer to this. My darling Brooke has came up with a joke. We have laughed and laughed at her. You would just have to hear her. I am not for sure what got her saying this. The only two things I can think of are, Courtney and her friends was telling jokes and maybe Brooke heard them. The other thing is a song from Barney that says "Why does the cow say moo?"
Brooke is saying cowboy instead of cow. Brooke started this yesterday and has not hushed yet. Finally today I said "We need a answer to your joke. This is our conversation.
Me: So you want to know why the cow says moo?
Brooke: Uh hum. Why does the cowboy say moo?
Me: Because God made it to.
Brooke: Because God made that cow to moo
So now Brooke is on the roll saying " Why did the cowboy say moo. Because God made it to"
This child is a mess. I told her that one time and she has not hushed. Her grandmother called and she had to tell her. She then had to call her daddy and tell him.
I guess this is Brooke's first joke she has came up with. Which it really is not a joke. I feel pretty sure she is trying to mock the way we was doing jokes in the van. For example why did the chicken cross the road, and all those silly kid jokes.
Brooke pays attention to everything. She has really got to where she ask questions. That scares me. I know I need to start her book about her being born. I think that would help when question times come.
This child melts my heart. She looked at me the other day and patted my face and said "mommy, you so pretty" I am thinking should I get her glasses. She then looks at me and says' I love you mommy". My heart was overflowing with joy and happiness. This little girl has brought so much sunshine to us. I thank God everyday for my little bundle of joy.