"We had a few tips off of film that we were able to differentiate between run and pass early," Dahl told CSNBayArea.com, referring to his former team. "So that kind of gave us an added benefit on defense.
"It was a few different things. Some different personnel and alignment stuff really were the big keys, as far as our giveaways."
Dahl, who signed a three-year contract with San Francisco this offseason, was a starter in the secondary for the Rams last season.
While the Rams finished with a 7-8-1 record last season, they played the 49ers to a tie and beat them in overtime in the other meeting. The 49ers averaged 18.5 points in the two games against the Rams, down from their 25.7 average in the other 14 regular-season games.
Dahl says now that he's a member of the Niners, he's already told his new coaches of the previous tendencies.
"It's been addressed and corrected," Dahl said. "They knew most of it before I even got here, and it's reconfirming. It's just on-going, self-studying and self-scouting stuff. Got that cleared up, too."