Transformers star Anthony Anderson was left red-faced when his teenage son shouted out his parents' safe sex phrase while dad was beating him with kinky toys.

The actor admits he was disciplining his son after he had been suspended from school - and, after chasing him into his bedroom, he started using items from his bedside "love chest" to "whoop his a**".

Anderson tells U.S. chat show host Arsenio Hall, "I coaxed him to run into my bedroom because I got this new toy that my wife didn't know about that I was gonna use on her a little bit later that night... It's a four-part harness unit that I restrain her by her wrist and her ankles, so it's under the bed ready.

"Little did my son know I'm surprising him with it now, so he jumps on the bed, I jump on his back, I throw the Velcro cuffs around him and he's looking at me, like, 'What the hell?'

"He's strong, he breaks one of the straps and kicks the belt out my hand. Our love chest is next to the bed, so I start digging in the love chest and whooping his a** with things in there - I'm pulling out boa feathers (sic), I'm pulling out soft leather straps... and I'm about to come down on him and my son just looks at me and his eyes go wide and he goes, 'Blueberry cupcake, blueberry cupcake...'

"I immediately stopped. I said, 'Oh my God, where did you learn that word (sic) from?' He said, 'I hear momma scream it sometimes and the noise stops...' Blueberry cupcake is our safe word."