Abou Diaby's Jekyll and Hyde personality on the pitch is well documented and discussed amongst Arsenal fans. However, it seems he has been drinking the potion more often than not this season and the French international has been prone to costly errors. The most notable is of course the inexplicable own goal at Old Trafford - a feat he almost repeated at AZ Alkmaar in last week's Champions League tie, only to have his blushes saved by the woodwork.
Then there was Sunday's game against West Ham.
Despite not being their fluent best, Arsenal were cruising on 2-0 at Upton Park with 15 minutes left on the clock when a foul by Diaby gave the home side a free kick just outside the box. Known for their vulnerability from set pieces, Arsenal conceded a goal as Mannone could only parry the stinging free-kick from Diamanti into the path of the lively Carlton Cole who deservedly got on the score sheet. Admittedly, that particular foul was a soft one - with Wenger calling it "a very generous decision" - but it was symptomatic of Diaby's play.
Arsenal started the game with their typical fluid passing movement, but West Ham was showing enough nous to suggest a potential upset. Cole was particularly menacing, holding up the ball and running at defenders well.
However, less-than-solid defending gave Arsenal two goals in the first half to perish those thoughts - at least for those who have witnessed Arsenal turn on the style and average three goals a game in their recent run. Another pasting was on the cards.
After the break, West Ham continued to fight and pressure the away team - Arshavin, the Russian master with super glue feet, giving the ball away numerous times was a sign if nothing else. Still, the away fans were cheering a string of passes as Arsenal comfortably kept possession. It was not to be another goal feast, but a win looked secure.
Then came along Mr Hyde. Already guilty of losing possession too many times while trying to dribble past three opposition numbers and making unnecessary fouls to give West Ham set piece chances, Diaby was again in the wrong place at the wrong time.
It is perhaps unfair to finger point at any one player but even Wenger, famous for not critisising his players, implicitly did just that in his frustrations when he said "We shouldn't have even have been tempted to give away a free-kick for their first goal".
West Ham, with their tails up, were putting pressure on Arsenal and were awarded a penalty when Song downed Cole in the area - a decision described as "super generous" by Wenger. Earlier, West Ham had a valid appeal turned down when there appeared to be contact from Gallas as Parker fell in the box, so perhaps Arsenal has little to complain about.
The finale was end-to-end as both sides threatened to sneak a win, with Van Persie coming closest with a header that was saved by Robert Green's trailing leg.
"There is no lethargy, the team wants to win and is focussed", assured Wenger as he dismissed suggestions that Arsenal's recent inability to hold on to a lead was a fundamental problem.
It was this time last year that a poor run of form all but ended Arsenal's tilt at the premiership title. Wenger is surely mindful of this and must be wishing the return to fitness of Denilson, a more consistent performer in the middle of the park, or perhaps even Nasri, who showed last season that he can play a more central midfield role.
Arsenal may have missed their chance to be 3 points off the top with a game in hand but they are still in a strong position to challenge for the title, but costly mistakes and late goals against must be stopped for that to happen.
It is time for someone to hide Dr Jekyll's potions.