The Bills held their second night practice of camp on Aug 1., and the defense was dominant for the second day in a row.

Buffalo’s defensive line continues to give the offense fits -- both the starters and reserves -- and the defensive backs have gotten their hands on more passes in recent days.

“They’ve done a good job,” coach Chan Gailey said. “The defensive backs are seeing a lot of things and reacting to the routes they’ve seen a lot of. They’re doing a good job of picking up on those things.”

What stood out: Safety Jairus Byrd was a difference-maker during team work. Byrd drilled receiver Derek Hagan on a pass down the middle of the field to create an incompletion; Hagan was OK and didn’t miss any practice time. Byrd later had an interception, and Hagan rebounded nicely with a leaping catch down the right sideline later in the evening. ... Defensive tackle Kyle Williams had a strong night, with several plays that would have likely been sacks under live conditions. ... After a terrific start to camp, T.J. Graham dropped a pass near the right sideline that would’ve been a big gain. ... Longshots Nick Saenz and Prince Miller both had interceptions. ... Mario Williams continues to impress, and Shawne Merriman had a couple would-be sacks as well. ... Both the first and second units struggled again in the two-minute drill. The first team’s drive ended with a Fitzpatrick fumble that Spencer Johnson took the other way for a TD; the second team’s drive ended with a Tyler Thigpen INT.

Backup QBs remain a concern: Both Tyler Thigpen and Vince Young continue to struggle. Thigpen worked with the "twos" on Wednesday, Young worked with the "threes." Accuracy has been an issue with both. Asked for his thoughts on Thigpen’s struggles, Gailey replied: “It’s a little early, but it’s a concern, and it’s not just Tyler. He and Vince are both having some trouble there. The 'twos' in general are not performing very well offensively. I think our 'ones' are doing some good things, but our 'twos' are struggling right now offensively.”

Injury updates: Linebacker Kelvin Sheppard was a new spectator, and the team was vague about his injury. Said Gailey: “He may be out a couple days, we’ll see. He’s got some situation that he’s dealing with. It’s medical, and that’s all I’m going to say about it right now.” Defensive tackle Marcell Dareus sat out the second half of practice, but Gailey didn’t believe it was anything serious. “Probably just giving him a rest of some sort -- I don’t think there was any real reason,” Gailey said. Eric Wood (knee) received a few more reps in team work. In addition to Sheppard, wide receiver David Nelson (knee), cornerback Justin Rogers (hamstring), defensive tackle Kellen Heard (ankle), safety Josh Nesbitt (undisclosed) and running back Chris Douglas (undisclosed) did not practice.

What’s next: Buffalo returns to the practice field at 3 p.m. ET on Thursday.

For more updates, follow Bills correspondent Mark Ludwiczak on Twitter @CBSSportsNFLBUF and @MarkLud12.