"I've been wondering 'Am I a man - or am I a dog?'" he says, smiling.
"And I've come to the conclusion I think I'm a bit of both."
Keith's rather odd bout of existentialist angst has come about due to his latest role.
The actor stars in The Call of the Wild, an adaptation of Jack London's classic dog story by Dom Douglas, in which family dog Buck is captured, caged and forced to fight against evil.
It's a great adventure story. But it's set in the snow-covered Yukon in the 1890s. How does this world possibly transfer to a a stage in Glasgow West End? And does a dog feature in the cast?
Is this too much of a stretch - even for the often clever Play, Pie and a Pint series?
"I play Buck," explains Keith. "But he's a man who works in an office, which he finds mind-numbing. And like the dog, he's a product of social conditioning. He questions his own lack of ambition and he rails against this.
"What I think the play is about is the realisation of potential, about getting out there and living your dream."
Keith adds: "It's a story a lot of people will identify with. Aren't we always hearing of those who give up the nine to five job to go off and become a karate teacher in the Bahamas?"
It's true. Yet, it will be a challenge, to capture the essence of Buck the dog and translate that into human form.
"I'm still getting my head around it all," he says, grinning.
Yet, all the signs are Keith will pull it off. As one of Scotland's most successful stage actors he has achieved great critical acclaim.
He loves to analyse the human condition and a hallmark of his performances is his keenness to get inside the mind of the characters he plays.
When the actor starred as Macbeth, he sought the advice of a psychiatrist to analyse the mental make up of the king.
What he came up with was Macbeth who was '"a bit Tony Soprano, a bit Malcom Tucker and a bit Walter White from Breaking Bad, a warrior, a good man."
Clearly, he loves deep, challenging roles.
"Yes, I've been called the Prince of Darkness," he laughs. "People have said to me I don't take on the obvious roles, but it's just the way my career has developed.
"When I began acting I did a lot of comedy. But then the likes of Peer Gynt came along and I loved getting into the depth of characters."
Doing Strindberg's Miss Julie, he asked himself several times during rehearsals, 'What am I doing?'
But if he didn't ask the questions he wouldn't come up with the layers needed to make characters jump off the page.
"It's all about taking risks," he say.
Keith grew up in Edinburgh and went on to study drama at Guildhall in London.
He spent seven years with Hamish Glen at Dundee Rep, learning his trade, going on to discover how to layer on characteristics via roles in productions such as Miss Julie, Barflies, Black Watch and Beautiful Burnout.
But in terms of The Call of Wind, he knows what it's like to work in a dead-end job.
"I once worked for a company that supplied fashion catalogues," he recalls.
"My job was to pick up cardboard all day long, fold it and put it into a machine that pulped it.
"I went to work when it was dark and got home when it was dark. And I hardly spoke to anyone during the day. As a result, it was a lonely, soul-destroying job, and it's that sort of working life which could make someone want to dream."
He adds: "Not that everyone has these dreams. But this play is about reflecting the thoughts of those who do. It's also about understanding that people work better if they are given a degree of respect."
Oran Mor's Call of The Wild reflects this.
"My character leaps around the office quite a bit," he says. "He's caged. And at times, what's going on in his head is brutal."
Did he ever think he'd become a dog, allegorically of course?
"No, I didn't," he says. "But it's a real challenge."
He adds, grinning; "And I'm certainly not playing Lassie."
n The Call of the Wild, Oran Mor, until Saturday.