Alan Quinlan: 'Back-to-back matches a cause for double-trouble with knowledge that there will be perfect chance to exact revenge'
We were seething. It was a great opportunity to win in France and we had blown it. Another promising European campaign was in jeopardy.
They bullied us, they got in our heads, they out-Munstered us.
Paul Volley lived up to his name, firing round after round of abuse, physical and verbal, at Ronan O'Gara, the No 8 knocking our chief playmaker off his stride - causing us to collectively trip over our own feet.
Sitting in that dressing-room in December, 2004, trying to digest how we had lost 19-12 to a Castres side we were confident of beating on their own turf, attention was already switching to eight days later.
They had won the battle but, there and then, we vowed to win the war.
Alan Gaffney and Brian Hickey, our forwards coach, lit the touch paper by claiming we had been soft. They twisted the knife to get a reaction, and boy did it work.
Just over a week later we bounced our French visitors around Thomond Park, cantering to a 36-8, bonus-point win.
And that's the beauty of these back-to-back games: the short turnaround allows sub-plots and rivalries to simmer away in a pot of intrigue and unpredictability.
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There was already bad blood between us and Castres before we were drawn together in 2004/'05, having been in the same pool in 2000/'01 and 2001/'02, us winning three of the four testy clashes.
You may recall that Castres No 8 Ismael Lasissi was initially given a 12-month ban for chewing on Peter Clohessy's arm in January 2002 before having the suspension overturned, clearing him to feature in our semi-final success four months later - a fifth showdown in 18 months.
Familiarity breeds contempt, as they say, so when we travelled to Stade Pierre Antoine 14 years ago, having narrowly won our opening two pool games against Harlequins and Ospreys, we were expecting the onslaught - but expecting it and dealing with it are two very different things.
I was on the bench for the first hour of the game, my blood bubbling after every late hit or spiteful barrage of verbals aimed at ROG and Peter Stringer.
The Castres plan revolved around unsettling us, so, cleverly, they went straight for our switchboard.
Volley, who knew us well from his time at Wasps, and France international centre Richard Dourthe led the assault.
Grinding my teeth on the sideline, I was already marking their cards for their visit to Limerick eight days later.
I took part in quite a few slogs over the years, but to this day I remember that those Castres games were particularly dirty.
I started the second game and was given strict instructions to protect ROG, ensuring my sideline study eight days previously would not go to waste.
My particular mission was to get in Volley's face, to disrupt the disrupter, which was a risky move by our management considering my tendency to overstep the line - not to mention the fact that I desperately wanted to knock the fella's head off. It was a sign of his effectiveness that he was highlighted as such a key figure.
We started slowly but once we hit our stride they couldn't live with us. We were wound up to the max.
Donncha O'Callaghan was shown a yellow card on eight minutes for throwing a punch in a ruck. It was a busy day for referee Roy Maybank.
Another old foe, Castres prop Mauricio Reggiardo, was sent to the bin for a stamp on 'Axel' Foley later in the first half.
ROG and former Ulster man Justin Fitzpatrick both also spent 10 minutes cooling down after a scuffle in the latter stages of the game, and Alessio Galasso, the third Castres prop to be shown a card by Maybank, was sent off late on for an off-the-ball incident.
There were scuffles all over the field from start to finish, late hits, stamping and sly digs at the breakdown - it was relentless. I was pretty pleased with how things were going midway through the second half only to receive a message from Gaffney that if I got involved in anything else niggly I would be taken off - which surprised me.
I was a bit disappointed in a way though because I thought I was doing a great job, although he could probably see my well-known red mist starting to descend.
None of it mattered in the grand scheme of things though, we got the result we so desperately craved and our hard-nosed reputation had been restored.
The current rivalry between Munster and Castres may not be so obviously fierce but you can be certain that there are a number of scores that players will be looking to settle over the next week.
I used to always prefer to play the initial back-to-back game away from home as being the host first up brings a different kind of pressure - and when you had as much confidence about playing at Thomond Park as we did, you always expected to at least share the spoils.
Johann van Graan's side are moving along nicely at the moment but early-season concerns around their away form have not been fully put to bed.
On paper, it looks like they should have more than enough to get the better of Castres in Limerick tomorrow but Christophe Urios is a clever coach who steered his side to a surprise Top 14 crown last season after finishing sixth in the table, taking out the top three seeds - Toulouse, Racing 92 and Montpellier - on their play-off run to glory.
French sides don't suffer from travel sickness as much any more, either, and while Castres lost at home to Agen last week - whose head coach these days is my old pal Reggiardo - and sit seventh in the Top 14, they have already won at Montpellier and Toulouse this season.
They may not have the star names or the lavish budgets that some of their Top 14 rivals flaunt, but this Castres side will be fuelled by something money can't buy - a desperation for revenge.
Every viewing of last January's 48-3 loss in Limerick will have poked the bear deep enough to cause bruising.
Remember, we were ready to combust after just eight days in between drinks in 2004.
After 11 months of fermentation you can be certain that Castres will be looking to prove a point tomorrow afternoon. Don't be surprised if you see some fireworks.