Wood felt his side were guilty of lacking intelligence in their most recent away game: the 20-9 defeat at Harlequins.
But they bounced back from the shocker at The Stoop with a nail-biting 16-14 win against a powerful Montpellier team at Franklin’s Gardens last Saturday.
And they will now aim to make it two wins from as many matches in this season’s Champions Cup by prevailing at Stade Pierre Antoine this weekend.
“We’ve got to box clever,” Wood said. “We’re not the biggest pack in the world and we’re not the biggest team, but we do back our fitness and mobility to play for 80 minutes.
“We’ve got to play for 80 minutes but if we don’t front up and be physical we know that when they bring the muscle you’re not going to win the game against a big French pack.
“We did well last weekend because they were licking their lips when the rain came down at half-time, but we were in the fight for 80 minutes and gave ourselves the chance to win.”
Saints have faced Castres on numerous occasions during recent times, squaring up to the French side eight times between October, 2010 and January, 2014.
So will those previous meetings help Jim Mallinder’s men prepare for this weekend’s reunion?
“I don’t know,” Wood said. “I guess you can bluff, double bluff and catch yourself second guessing.
“They’re a quality side but we are familiar with some of their individuals and we’ve got to back up last Saturday’s performance.
“What we have got to learn is how to play away from home.
“I don’t think we were very intelligent against Harlequins. We did some good stuff, but we played in the wrong areas and we made some individual errors when we just needed a foothold.
“We’ve got to improve on those things and we’ve got to recognise what a narrow margin last weekend’s win was and make sure we’ve got a bit more in the bag by the last couple of minutes than there was last weekend.”