ACT Brumbies coach Jake White can tell them apart by looking at a broken nose while their teammates are enforcing a rule that one of the Smith brothers must always have shaggy hair.
Now Ruan and Jean-Pierre Smith are on a mission to send the British and Irish Lions into a twin spin at Canberra Stadium on Tuesday night when they combine in a dream Brumbies call-up.
The two South African-born props are set to team up in the Brumbies' front row for the first time as the ACT side searches for a historic win against the Lions.
Sure, their experience totals just six Super Rugby games - all Ruan's - and the Lions boast the best set-piece exponents in the world.
But the Smiths say their secret weapon is confusion. No one can tell them apart. They were born three minutes apart, play in the same position and even answer to each other's name.
''Our coaches in Brisbane used to say, 'I don't know which brother you are, but one of you did a good job','' Jean-Pierre said.
''People call me [Ruan's] shadow because we're always together. We don't plan to do it, but it's just the way we are. I used to grow my hair longer so they'd know which one I was … now down at the Brumbies I've got to keep it that way.
''A lot of props get confused when they look at us in a scrum … Two months ago I never thought I would be here, words can't describe how I'm feeling.''
Spare a thought for hooker Siliva Siliva when he packs down between the identical brothers against the Lions.
Siliva has never played with twins before. He admits he's confused when they prop up under his arms.
''Telling them apart is one of the toughest things for me in the game … the only way you can tell is their hair,'' Siliva said.
''The Lions will definitely get confused. We do at the Brumbies, so they definitely will.''
Prop Scott Sio will return from Wallabies camp, but Dan Palmer is battling a foot injury and it is unclear whether he will play.
If Palmer is out, it is likely White will call on a club rugby front-rower from Easts to fill the void as the fourth prop on the bench.
Ruan is in his first year at the Brumbies after starting an extended player squad contract.
Jean-Pierre moved to the capital only recently and will take Ruan's extended player squad contract next season when his brother is upgraded to a full-time deal.
The 23-year-old Smith brothers do everything together. Jean-Pierre has been staying on the foldout bed at Ruan's place since arriving in Canberra and they regularly cook up a ''braai'' - a South African barbecue - with housemate Etienne Oosthuizen.
While Ruan has been a front-rower his entire career, loosehead prop Jean-Pierre flirted with a move to the back row before rekindling the family partnership.
Tighthead prop Ruan earned praise for his barnstorming performance against the Melbourne Rebels on June 7 and commentators described him as a ''runaway bull'' as he trampled over defenders.
He is 188 centimetres and 119 kilograms, giving him a slight edge over older brother Jean-Pierre (185 centimetres and 115 kilograms).
Because their family moved to Brisbane in 2010, they are eligible to qualify as Australian players.
Ruan has the rare achievement of representing two countries at schoolboy rugby level - Australia and South Africa in consecutive years.
''I didn't think I'd play any games this year let alone a chance to play against the Lions,'' Ruan said.
''I've played all my rugby with JP. All the way from primary school to senior rugby. It doesn't matter if our teammates yell out 'JP', I automatically look because I think they're talking to me.
''When Jake told me JP was going to come to Canberra … it made everything easier because we've been together our whole life. I missed home a lot, but with him here it's easier.
''A lot of people think we're competitive, the [teammates] always joke who's better looking but we've always got a comeback.''
The duo cut their teeth and one of the most successful rugby schools in South Africa, Paarl Gimnasium, the same school that produced Springboks Jean de Villiers and Schalk Burger.
White has a soft spot for the pair. He watched them grow through the junior ranks in Cape Town and one of the first things he did when he arrived was ring Ruan.
''I've known them from school. The day he became Aussie-eligible we chatted and Ruan joined us. Who would have thought they'd be playing against the Lions?'' White said.
''It's a great success story for both of them. This is what they always would have dreamt about in South Africa.
''Yep, I can tell them apart. One has a broken nose … if you look carefully, JP's nose is a bit crooked. But if they put caps on you wouldn't know the difference.''