Donncha O'Callaghan is reneging on his former life as a practical joker. It potentially represents a conversion of Damascene proportions.

At least the 25-year-old bowed out in style. Although reluctant to recount the adventure, he concedes that his curtain call as a practical joker came on a Munster trip to Sligo. Having been alerted to a Munster management team meeting in a particular room, O'Callaghan and his partner-in-crime - we'll just call him Aussie Dave - shepherded a group of 12 ducks into the room prior to management's arrival.

Unfortunately the ducks became a little flustered in the confined space and some small deposits betrayed those nerves.

O'Callaghan winced: "Jerry Holland stood right beside as I cleaned the place from top to bottom."

Maturity is a factor, but the affable Cork Constitution second row didn't need to be brow-beaten into the change. A sin-binning in last season's epic European Cup semi-final against Wasps at Lansdowne Road - it should be pointed out it was for cumulative transgressions by the team and he just happened to be the unlucky next transgressor - precipitated the change.

"That was hugely disappointing and it made realise how important rugby was to me. I didn't really want to experience that feeling again, and maybe that's been the catalyst."

Educated at CBC Cork, he won a schools cap against England at Lansdowne Road in March, 1997. He played alongside Damien Broughall in the second row on the Ireland team that won the Under-19 World Cup in Toulouse in 1998, beating France 18-0 in the final.

Arguably one of his finest moments at underage level came while playing in the Under-21 World Cup in Argentina in 1999. In a pool match against the All Blacks, O'Callaghan, playing at blindside flanker, turned in a momentous display, eliciting praise from the New Zealand coach.

In November 2000, he represented Ireland at Under-25 level against Japan, and 12 months later he lined out in the Ireland Development XV's game against Samoa in Donnybrook.

His first A cap arrived when he came on as a replacement against Scotland in March, 2002, before a winning his first senior cap a year later as a replacement against Wales in Cardiff.

He won seven more caps coming off the bench before earning his first start in the Six Nations game against Wales last February.

Injury towards the end of last season delayed his competitive debut in their current campaign, although not to the same extent that some believe.

"I think that people feel I might have fallen off the end of the earth during that period. All it did was extend my pre-season by four weeks. Or at least that's the way that I approached it.

"It allowed me to do a lot of work in the gym, the first time that I was able to do serious pre-season work since my days in the academy."

Saturday provides him with an opportunity to road-test his new body shape and to enjoy the physical release of stepping back into the Test arena.

Last season, along with Paul O'Connell, the Munster second-row duo blitzed opposing lineouts, and O'Callaghan began to deliver consistently on his underage potential.

He got off to a slow start in terms of game time this season, but the Americans will provide a barometer of his battle hardiness. Malcolm O'Kelly has thrown down the gauntlet in terms of performance.

A new haircut has been unveiled to go with a more "serious" approach, but one can't help the feeling that the leopard won't get rid of all his spots. That would be a pity.