The Browns' offensive line is supposed to be one of the strengths of the team, but its Achilles' heel has certainly been exposed this season.

The O-line has been embarrassed by 4-3 defenses with active fronts. That's why the Carolina Panthers (1-9) could pose a serious threat today. Their defense fits the description of those that have wreaked havoc against the Browns (3-7).

Panthers coach John Fox had his poker face on when he said he didn't view the Browns' blocking against 4-3 fronts as a deficiency. But you can bet he studied how the Atlanta Falcons and the Jacksonville Jaguars used stunts and slants to dominate the Browns in the trenches.

''The communication is huge,'' Browns left tackle Joe Thomas said. ''It's everything really, especially against the 4-3, because you need to be on the same page with the guys next to you in order to be able to pick up the stuff. A lot of times it is switching assignments, you're switching gaps, so it's all about communication. It's all about pre-snap reads.''

Throughout the season, the majority of the Browns' opponents have employed 3-4 defenses. Blocking against a 4-3 isn't rocket science, but apparently it presents enough challenges.

In Week 5, the Falcons held the Browns to 48 yards on 20 carries (2.4 average). Without a viable rushing attack, the Browns put themselves in a tough spot.

The Falcons' pass rushers teed off, recording three sacks and five quarterback hits. As a result, Seneca Wallace suffered a high ankle sprain and fellow quarterback Jake Delhomme reinjured his mangled ankle.

Last week, the Jaguars' defensive line followed the Falcons' recipe for success. The Jaguars limited the Browns to 88 yards on 26 carries (3.4 average). Keep in mind, 39 of the 88 yards were a result of rookie quarterback Colt McCoy avoiding pressure and gaining ground.

Speaking of McCoy, he was sacked six times, hit at least twice more and left hobbling away from EverBank Field with a walking boot on his left foot and a cowboy boot on his right foot. Yes, another tenacious defensive line in a 4-3 system left another Browns quarterback with a high ankle sprain.

Now with Delhomme back in the fold, what can the O-line do better to protect him against his former team?

''You can't let them penetrate into the gaps,'' Browns coach Eric Mangini said. ''You've got to be able to blunt it before they get into the seam between the offensive linemen. When you blunt them and they're moving, a lot of times what happens is you just use their momentum to wash them down the line of scrimmage and you can create some big plays.''

The Browns' offensive linemen could have used an excuse along these lines after their loss to the Jaguars: ''We had rookie Shawn Lauvao making his first career start at right guard, and John St. Clair was coming off an injury to play right tackle because Floyd Womack was sidelined. That's why we weren't on the same page.''

To their credit, they didn't play that card. Making excuses won't help them execute a turnaround against the Panthers. Instead, they must focus on solving the great mystery of the 4-3.

''If you're sound fundamentally in the pass game, it's a little bit easier [to block against them] 'cause you're not attacking, you're backing off in the pass game,'' Thomas said. ''So when they're twisting, they're kind of passing themselves off. In the run game, you're trying to attack them. If you're not good with your eyes and your feet and your communication, you can get picked off before you get a chance.

''In Jacksonville, we had the opportunity to keep running it because the score was close. That was frustrating, 'cause we had a lot of runs, and we weren't able to make it work. This week we're gonna try to make sure it's different.''