Dahl, a starter for the Rams at safety last season, signed with the 49ers as a free agent this offseason. He told CSNBayArea.com that St. Louis "had a few tips off of film that we were able to differentiate between run and pass early," giving the Rams an "added benefit on defense."
Dahl's claims caught the eye of Finnegan, a starting cornerback on the Rams, who responded with a Twitter message Wednesday to ProFootballTalk.com, which was published by the website.
"Craig Dahl is lame and weak for that glad he with another squad we know how he play thanks for the tips we know who 2 go at," he wrote.
He followed that up later with a tweet vowing that the Rams' offense would target Dahl to exploit the 49ers' defense this season.
"Craig Dahl we know how you play thanks for the tips we know who to attack early and often," he wrote.
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 ongoing, self-studying and self-scouting stuff. Got that cleared up, too."