Ventimiglia told Kimmel on Thursday that looking the dog in the eye would cause the canine to look away, ruining the scene they were shooting.
The actor would then discover from the film's dog trainer that he needed to look elsewhere
"She goes, 'Were you looking the dog in the eye?' and I go 'Yeah.' She goes, 'You are his alpha, he won't challenge you. So look him in the center of the forehead, look him in the ear but don't look him in the eye,'" the actor said.
The Art of Racing in the Rain, based on the Garth Stein book of the same name, is set to arrive in theaters on Aug. 9.
Ventimiglia also told Kimmel that he grew attached to one of his dog co-stars, but that the canine already had a good home.
"This dog just had the most beautiful soul and he had the best temperament," he said. "He was my guy."