Use details from Old Yeller to describe Arliss.

Arliss is Travis's little brother. We are told in chapter one that Arliss is five years old, and readers will learn throughout the story that Arliss is a fairly typical stock little brother. He loves Travis dearly, and he looks up to his older brother with deep affection and respect. However, that doesn't mean Arliss doesn't bug his older brother.

I said: “Arliss! You get out of that water.”
Arliss turned and stuck out his tongue at me.
“I’ll cut me a sprout!” I warned.
All he did was stick out his tongue at me again and splash water in my direction.

The above quote does a nice job of showing how Arliss likes to intentionally get Travis going, but it also shows that Arliss can be a great mixture of mischievous and hilarious. In addition to those traits, Arliss is a very confident five-year-old boy who is not ashamed of his body. For example, Travis eventually chases Arliss out of the water, and a completely naked Arliss runs into the house screaming "bloody murder." Finally, Arliss is a brave and fiercely protective boy. He is this way with his family and with Old Yeller.

He ran past me and fell on the dog and petted him till he quit howling, then turned on me, fighting mad.
“You quit kicking my dog!” he yelled fiercely. “You kick my dog, and I’ll wear you to a frazzle!”
The battling stick that Mama used to beat the dirt out of clothes when she washed stood leaning against the wall. Now, Little Arliss grabbed it up in both hands and came at me, swinging.
It was such a surprise move, Little Arliss making fight at me that way, that I just stood there with my mouth open and let him clout me a good one before I thought to move.