Expect the unexpected
Former Dublin star Cahill believes Donegal will 'try something unusual' to upset Dublin's plans
For obvious reasons, Donegal form something of a dark presence in the Dublin footballing psyche.
Their recent historic propensity for dropping nuclear tactical bombshells has ensured an uneasiness around the capital ahead of Saturday evening's All-Ireland quarter-final.
Even if Jim McGuinness and his mystique are no longer opposing forces.
Rory Gallagher was, according to innuendo from some of the anti-McGuinness faction within the county, the strategic mind behind much of what was effective about Donegal prior to the pair's falling out after the 2013 season.
Which, even if only partly true, brings a new layer of unpredictability.
"When he sat down to plan for the year I'm sure he felt they would have to play Dublin at some point to get to an All-Ireland final or win an All-Ireland," reckons former Dublin senior, Barry Cahill, who played with Gallagher at club level with St Brigid's.
"So I think he will try something unusual."
In 2011, Pat Gilroy's team flirted skittishly with disaster before delivering a sort of coming-of-age finish to that infamous All-Ireland semi-final.
But the sheer ugliness of that game, and Dublin's proximity to disaster therein, cast a pall over the afternoon.
According to Cahill now, Dublin considered it "such a freak game" that "we didn't even analyse it," in the build-up to the ensuing All-Ireland final "because it was such a once-off".
More recently, McGuinness masterminded arguably the greatest coup of his excellent tenure which firstly, highlighted the folly of Jim Gavin's team's brilliant but predictable attacking play.
More recently, it's partly credited for spawning the more controlled version of the team that won last year's All-Ireland.
That performance was, Cahill says, Donegal "playing at their absolute peak.
"Phenomenal performance and Dublin got caught a bit cold. The offensive play they (Dublin) had at that time was so strong they probably did neglect their defensive duties."
In the weeks after, Jim Gavin publicly accepted the blame for that loss and its manner.
"On a personal level, I accept full responsibility for that performance," said Gavin then.
"And I accept full responsibility for the philosophy and for the way Dublin play their football, for the attacking style we play and sometimes for the vulnerability that it brings."
As Cahill notes, Dublin "have tidied that up over the last 18 months.
"But I think it will be tough on Saturday I really do."
Last Saturday, after Donegal made sure of the fixture with victory over Cork, Gallagher intimated that he had kept his team on a leash in their two league matches against Gavin's men this spring, a view Cahill endorses.
"As soon as he came into our club in 2002," Cahill says of Gallagher, "he nearly became player-manager at one stage - he was that vocal In training, in the drills that we did, in the tactics, video sessions, you could see straight away that he had the mindset of a coach from his mid-20s onwards.
"It was no surprise that he took to management like he did.
"I don't think Donegal showed their hand in either League game," he adds, "and I have a feeling we will see something on Saturday evening that will cause Dublin a bit of bother."
In McGuinness's Irish Times column, he has suggested repeatedly that Dublin could be exposed aerially by the deployment of two target men.
Rory O'Carroll's absence has only increased this belief.
"If they do go with that then Cian O'Sullivan will drop that bit deeper which will give them the chance to have a runner or an overlap in the middle third which Donegal are brilliant at," Cahill points out.
"Rory is such a huge loss and Dublin have coped quite well so far and Davey Byrne has been excellent.
"But the two big men in the full-forward line would be something Dublin haven't encountered before.
"And thinking about the squad they have it would be difficult for them to replicate that in training matches.
"The Cian O'Sullivan factor is interesting as well," he adds.
"Cian is a phenomenal footballer but at times he looks in cruise control. Nobody is really targeting him or putting him under pressure.
"But look," Cahill concludes, "it's hard to predict.
"But I just have a feeling Donegal will come with something new."