Fields' famed exhortation to all thespians to avoid working with scene-stealing animals and children gets no respect from Reinhold, who finds the huge, slobbery Beethoven a rollicking good companion.
Indeed, so enamored of the outsized galoofer is Reinhold that this is his second movie with Beethoven; the first being "Beethoven's 3rd."
Why has Reinhold, an extraordinarily fine actor, chosen to ignore the bibulous comedian's admonitory words about appearing on screen with a canine?
"I refuse to be intimidated by W. C. Fields' remarks," Reinhold said this week, grinning.
"I try to hold my own with both kids and animals. Charles Grodin did the first two 'Beethoven' films and decided not to do the third one.
"When they offered the role to me, it was a lucrative deal and I talked to my wife (Amy) about it. She said, 'As silly as it is, what could be more important than making kids laugh?'
"So it's not a big prestigious film about a cross-dresser who's ostracized by a town or something. She convinced me making children laugh was just as important as making a strong social statement.
"I feel she's right. It has been gratifying to have kids approach us and look at me with affection."
Both his "Beethoven" films have been made for video only and are runaway hits.
As a serious and successful actor with such films as "Fast Times at Ridgemont High" and "Beverly Hills Cop" to his credit, Reinhold finds himself as much at home on camera with his large pal Stanley in the role of Beethoven.
"When you work with a dog, you have to be very loose because you're a straight man. You play off the dog's reactions.
"You have to take an improvisational approach to the situation to allow the dog to provide you with some good stuff to play off of.
"I was disappointed they didn't use some of the stuff, but they didn't want to veer too far from the script.
"It's fair to say I really like Stanley and he likes me. It helped us work well together. It happens. Think of Tom Hanks and that dog in 'Turner & Hooch.'"
Reinhold off-screen is an extension of the characters he plays in his films. There is no theatricality about him in any case.
He is a masculine, straight-shooting guy who epitomizes the American male helping to hold up the world -- a reliable actor superlative at underplaying roles to allow audiences to suspend their disbelief.
Reinhold and Bill Pullman often contend for the same roles because both represent unprepossessing males behaving intelligently, not some doofus or breast-beating macho hero.
Time and again Reinhold has proved his mettle. His 65 movies include "Ruthless People," "A Soldier's Tale," "As Good as Dead," "Wild Blue" and "Walking Across Egypt."
He and Amy make their home on an acre and a half in a village near Santa Fe, N.M., far from the bright lights and night life of the movie colony.
His remote lifestyle doesn't hinder his availability for movies. He just hops on a plane and in a couple of hours can be found in a Hollywood office or sound stage.
The tall, spare Reinhold cherishes a private life.
He is not a movie star, but an actor dedicated to his work, free of the frequent mania of performers with an overweening desire to be in the public eye.
It amuses Reinhold that although Pullman made his film debut in one of his pictures, he lost out to Pullman to play opposite Meg Ryan in "Sleepless in Seattle."
Reinhold has mastered the art of non-bravura acting. On camera he maintains the demeanor of a man caught unaware of his own presence.
"You have to be aware of your audience," he said. "'Beethoven's 4th' is a kids' movie, a cartoon, and I play a loving dad who has some funny moments with the dog.
"It's fun. The premise in 'Beethoven's 4th' is that Beethoven has been switched with another dog from a rich family. Suddenly the dog is very well-behaved and quite unlike the Beethoven we've known.
"We used two different dogs. The replacement had to be well-trained, and Stanley is a slob.
"The picture is total farce, which is a change for me.
"The element I'd most enjoy about stardom would be the luxury of working with people like (director) Steve Soderbergh. I take the best I'm offered and make the best of it.
"I turn down scripts that are exploitive or really violent for no reason, stuff I don't feel comfortable with if it offends my sensibilities."