Sharing.

AW is always policing his little brother to make sure he's not having any fun.   AW especially doesn't like when DW touches his things.  (Well, in all honesty, AW doesn't like when DW touches any thing.) No matter what his little brother has in his hands, AW stomps over, grabs it from him, and says, "MINE."  Then he puts the item somewhere out of DW's reach.  DW gets mad and swears his revenge.

DW is on a mission to touch all of AW's stuff.  He loves sneaking into AW's train stash and licking all his Thomas the Tank Engines.

AW:  "No!  Mine!"

Because we tell AW that he has to let DW lick his things, he has come up with a new strategy to irritate his little brother.  He thinks, if you touch my things, then I will touch all of your things. I will read Orbit in your Rock N Play.

I will watch Paw Patrol in your Bumbo seat.

I will lounge happily in your swing.

And...well, you get the picture.  Little does he know that his silent protest has little to no effect on DW.  He is still going to touch everything.  

 And put it in his mouth.

That's what little brothers are for - making sure your cool stuff has a good coating of baby saliva on it.