Midway through the first half of an Arsenal game earlier this season, a club employee turned towards two of us sitting behind him and produced a grimace worthy of something from Wallace & Gromit.

Arsenal were not losing, in fact they would go on to win, but there was an uncertainty to their play that left even the invested unconvinced.

It turned out to be one of the matches in a long unbeaten run,

one that stretched to 18 on Thursday night in Ukraine. Eighteen games undefeated, dating back to August, that is noteworthy. It has those who see football through statistics alone shouting about the impact of Unai Emery.

In moments like this, the uncovering of a manager’s ‘secret’ is always sought and, sure enough, Emery’s banning of sugary fruit juice from the training ground was produced as an example of attention to detail.

It is all part of the show, the propaganda as Gordon Strachan calls it. Maybe it helps but it is the sort of anecdote that drags focus away from the pitch, albeit temporarily, and skews the reality, which is that Arsenal’s 18-game stat does not tell anything like the whole story of their season.

On Thursday night, for example, Arsenal won 3-0 in the Europa League against a team called Vorskla, who are 17 points behind leaders Shakhtar Donetsk after 16 games of the Ukrainian league. Vorskla were denied use of their home stadium by the introduction of martial law and, having sold 25,000 tickets, one of the biggest football night’s in their town’s history.

Moved to Kiev, their anticipation flattened, Vorskla were so weak Arsenal were able to finish the 90 minutes with six teenagers. Their youthfulness became the storyline of an undramatic evening.

Emery acknowledged his young boys, but it would a surprise if he thought here was a meaningful occasion for the team he has inherited after 22 years of Arsene Wenger. It would a surprise if he thinks it relevant to meeting Tottenham in the north London derby on Sunday.

For a start, Arsenal may have only one starter from Kiev in their line-up tomorrow. Then there will be the sharp difference in the quality of opponent and, thirdly, Spurs will hardly set up as two banks of four hoping to play breakaway football. These differences eat into the idea of the 18-game run as a sequence to behold.

Tottenham’s aim is likely to be – or should be – disruptive. Unsettle Arsenal, test that uncertainty, make Gunners’ employees shift in their seats.

Mauricio Pochettino’s team has the ability individually and collectively to do it. They are, moreover, a unit forged over four and a half years together under the Argentinian. Emery has been at Arsenal six months.

Although praise for Spurs under Pochettino has sometimes outstripped achievement, they finished 14 points ahead of Arsenal last season, three points more than the year before. That is why “power shift” talk has gathered pace. It would have increased further had Tottenham possessed the logistical competence to be in their own stadium on time.

They remain at Wembley, where last Saturday they put three past Chelsea, previously unbeaten and flowing.

It must be said an idiosyncratic defensive display from David Luiz contributed to Tottenham’s victory, but the verve of Eriksen-Kane-Son-Alli makes it difficult to conceive the visitors leaving Arsenal on Sunday without a goal. Spurs have failed to score in only one of 20 games this season – against Manchester City. Arsenal’s last clean sheet in the Premier League was in September.

It all adds up to a tricky afternoon for Emery and if reports on Monday morning say Arsenal’s run is at 19, the Spaniard can be pleased.

Because another Arsenal run to contemplate is their recent record against the other five of England’s ‘Big Six’: Arsenal have lost their last four games against Manchester City, have beaten Chelsea once in the league since 2010, have not beaten Liverpool for three years and have won two of the last 14 in the league against Manchester United.

There was at least a farewell-to-north-London derby win for Wenger against Spurs last November. But, overall, Arsenal’s peer-group failings are obvious.

Does that matter as much as Bournemouth having an onside goal ruled offside at 0-0 last Sunday?

People read a new defiance into Arsenal’s 2-1 win against Eddie Howe’s team. That seemed like over-interpretation and it would be dangerous for Emery to share it.

This may sound like a lot of doubt with which to confront a team on an 18-game unbeaten run. But it will take a statement performance from Arsenal to wrong-foot doubters.

It would be timely: Spurs is the first of 10 games in 30 days, the next of which is at Old Trafford on Wednesday. True, Arsenal have not lost since August, but here comes December.