Just before he falls asleep, he still can be distracted if you tell him about the Bus with wheels that go round and round, the driver says, "Move on back" the babies say "Wah", the mothers say "Sh!", the wipers go swish, etc!
 

You'd never believe the antics required by adults to achieve this happy face!  We were dancing, singing, and saying "chug-a chug-a chug", wipers go swish, mothers say sh!  The photographer must have thought we were crazy!  (Christy, Mark, Dave, Val, Tom and me!