We don't know if they will be needed.
But we do know that, should a penalty shoot-out be called for late into the night in Lansdowne Road this evening, the Ireland squad - good students that they are - have done their homework but the Danes haven't bothered.
Having already told the media that he had done "nothing" in terms of extra work on penalties since Saturday's 0-0 draw in Copenhagen, Denmark boss Age Hareide was asked by The Herald if that was down to superstition, or because he didn't think penalties would be needed?
"Both," he said with a smile. He knows one goal should be enough for his side as he does not expect Ireland to score twice so penalties are not in his schedule.
O'Neill has already planned for the eventuality. "Yes, we practised penalties and Meyler missed," he said of the Hull City player seated right beside O'Neill.
"Taking penalties in practice is totally different to taking in the game. It's on the evening. We've done it umpteen times before, as player and manager, generally those lads who volunteer in practice don't take them in matches.
"Remember that great final, Liverpool and Roma, couple of great Brazilian players downed tools," says memory man O'Neill of the 1984 European Cup final, played in Rome, a total of three Irish players (Mark Lawrenson, Ronnie Whelan and Michael Robinson) involved as the Reds won on penalties.
"We have people like Meyler who want to take them, that's half the battle."
So who would take Ireland's spot kicks? Robbie Brady took one, and scored it, against Euro 2016 hosts France last year. Months earlier, James McClean took one and scored in a friendly against Slovakia. Add in Meyler and that's three.
But the men who scored Ireland's other penalties in recent years, Robbie Keane and Jon Walters, are not around.
Harry Arter took a dreadful spot kick for Bournemouth against Southampton last season, around the same time that Shane Long missed the target with a penalty, for Southampton against Middlesbrough. Would those missed chances keep them from putting their hands up? Or would someone like Stephen Ward or Cyrus Christie insist?
The Irish national team has only had two experiences of penalty shoot-out situations.
One good: Italy 1990, when Packie Bonner saved from Daniel Timofte, David O'Leary stroked the ball past Silviu Lung as the nation held its breath and then celebrated.
The other one? Not so good, when Mick McCarthy's team were beaten on penalties by Spain in the last taste of world Cup football proper for Ireland, north or south.
So Ireland have had many experiences in play-off games - cops in Bursa, crazy fans in Tehran, poor-sighted match officials in Paris but penalties have never come our way in this scenario before.
But a penalty shoot-out could arise tonight, and that could suit Meyler, who has been on spot-kick duties for his club of late.
"I'm in charge of taking penalties now," he said of Hull, before Ireland had made the play-offs. "Our penalty taker was injured and I happened to be on the pitch.
"I've taken penalties before in penalty shoot-outs so I said I'll take it because we didn't have a designated penalty taker. I scored and once you score you stay on penalties.
"It's nearly like a free goal in the sense that if you do everything correctly you can't really miss. It's practice and just being confident striking a ball. Obviously, there are different occasions.
"If you're talking a Champions League final and it goes to a penalty shoot out that's a little bit different. It's a big occasion and if you miss you could end up costing your whole team. But if you do everything right I think you should score."
Tonight could put that theory to the ultimate test.