Effect: Jack wants to get away from a conversation with Julian and Miles about snow sledding. Cause??

From the text:

"I left my old sled there," said Miles. "It was the crappiest piece of junk—and someone took it, too!"
"Maybe a hobo wanted to go sledding!" laughed Julian.
"Where did you leave it?" I said.
"By the big rock at the bottom of the hill. And I went back the next day and it was gone. I couldn't believe somebody actually took it!"
"Here's what we can do," said Julian.
"Next time it snows, my dad could drive us all up to this golf course in Westchester that makes Skeleton Hill look like nothing. Hey, Jack, where are you going?"
I had started to walk away.
"I've got to get a book out of my locker," I lied. I just wanted to get away from them fast. I didn't want anyone to know that I was the "hobo" who had taken the sled.