Why does grass grow?

I had some alone time with each of the big boys today.  Bee and I did puzzles and read books while Bean was napping and LM was at school, and then LM and I had our standard afternoon "quiet time" while his brothers napped.  I've started a reading project with him, where we read a few chapters from a chapter book each day that I'm there and it makes him so happy that I feel like a super nanny for coming up with the idea.  Our first book is The BFG, by Roald Dahl, and LM loves it.  We read at least thirty pages every afternoon I'm with him (that's a whole lot of attention span for a four-year-old).  Anyway, I tried hard to remember some of the dialogue that goes on between me and the big boys - especially when I'm with them one on one - because it's so hilarious and needs to be shared.

Me: Hey Bee, do you want to do your Thomas puzzle or your dinosaur puzzle?
Bee: Yes I do!
Me: Which one, sweetie?
Bee: Yes I do!
Me: Okayyy, why don't we do Thomas first and then dinosaurs?
Bee: Bee wanna do dinothaur puzzle FIRTHT.
Me: Ok, dinosaurs first it is.

I have no idea why my little guy refers to himself in the third person, but it's hilarious.  I think it's a language developmental stage that kids go through, as they learn to identify first and third person, as well as correct pronouns, but regardless, it's adorable.

Then, this afternoon, the "lunch rush":
"Bee, do NOT pour your water into your plate or you will go sit on the thinking bench."
"LM, sit. on. your. bottom."
"Bean!  Please ingest this!  I am not an endless supply of chopped ham particles for your throwing enjoyment!"
"Caywin, may I pweeze be 'scused?"
"Yes, good boys, let's go wash our hands."

Then Bean and Bee go down for naps, and I spend a good half hour cleaning up after lunch while LM plays and asks me things.  When I finally sat down to have a glass of water, post-cleaning, this was the conversation that played out:
"Caywin, why does grass grow?"
"Well, it's a plant, and plants grow on the earth just like people and animals do."
"But where is it okay to ride your bike on grass?"
<Is that the definition of a non sequitur?  A four-year-old?>
"Um, well, it's probably okay to ride a bike on the grass if you lived in a place where you owned the grass.  Like a house with a lawn."
(Keep in mind, I am trying to describe suburbia to a four-year-old who's been raised in Manhattan.  He doesn't know what a lawn is, unless we're talking about the Great Lawn of Central Park, on which bikes are most definitely not allowed.)
"But why is a bike bad for grass?"
"Because the wheels crush the grass blades and make it hard for them to grow."
"So driving a car would be really, really bad for grass."
"Yes, yes it would."
"But walking on grass doesn't hurt it?  Because our shoes have holes in the bottom?"
"Um...well...technically, I suppose walking on grass does hurt it a little bit, but it recovers okay.  Grass is tough stuff."
"But bikes.  They're not allowed on grass."
"That's right, bud.  Bikes are bad for grass."
End scene.  Note: I don't have a clue who or what mentioned grass, bikes, shoes, cars, etc to LM today or if he just came up with it all on his own.  He's four.  That's all there is to it.