SUMMARY: Running dogs.
This time, Chip is chasing Luke. Sometimes it's the other way 'round. For several days, Luke didn't do the tunnels at all. Then he walked through the straight one (in the background) a few times on his own, then for a few days, during chases, he'd run through it, back around, and through it again, repeat repeat repeat. I finally saw him walking into and through the curved tunnels a couple of times. Running through these other tunnels is new today as far as I know!
(Chip already had been doing some running w/Luke and chasing the dog next door and is tiring out, so this isn't the full-blast chase.)
Luke learned the tunnel running during chases from Chip. He also learned the going back and forth inside from Chip.