Ireland flanker Tommy O'Donnell knows more than anyone that being named on the bench doesn't necessarily mean an easy 20 minutes.
The young Munster forward has impressed twice in this Six Nations when having been called upon to replace Sean O'Brien.
O'Donnell replaced O'Brien after the experienced openside dropped out of Ireland's opening match with Italy just before kickoff, before coming on after 20 minutes to replace his compatriot in last Sunday's big win over England.
Learning to handle sudden introductions after his two so far, O'Donnell excelled again for Ireland.
The 23-year-old described both matches against the Italians and English as being extremely physical, with more of the same expected when Ireland take on Wales.
"I suppose if you can come in off the bench straight off the warm-up, it's not going to get much harder than that," said O'Donnell.
"Coming off the bench after 20 minutes (against England), I was thinking, 'okay, I've done this before'. It was just a matter of slotting in and doing what I do, going about it to the best of my ability.
"I found the Italian game incredibly physical, trying to attack them. The English lads are big ball carriers. Maybe missing out on that first 20 minutes, that's where it might have been a lot tighter. It was physical, but it was on a par with the likes of the Italy game.
"Wales are a good attacking side: they went to France and beat France. That's a fair achievement, so they've got very big ball carriers, incredibly physical players and they're quite mobile and agile.
"They don't take any prisoners in their pack; they're great defenders and good at the breakdown. To go over there to Cardiff will make it a small bit tougher."