ST. LOUIS (AP) ― The mass shooting at a Colorado movie theater rattled the nerves of some other moviegoers with opening weekend tickets for the new Batman film and led some cinema chains to add more guards. Experts say it’s unlikely, though, that venues will implement even stricter security measures because it would significantly alter the experience of going to a film, concert or game.

The early Friday rampage in Aurora, Colorado, at a midnight screening of the new Batman movie, “The Dark Knight Rises,’’ left 12 people dead and dozens wounded. Authorities say the gunman apparently slipped out through an emergency exit to arm himself, then re-entered that way and opened fire on the startled audience.

The attack had a chilling effect on some ticketholders who had been eagerly awaiting what had been billed as the summer’s hottest movie.

“I’m just going to keep my eyes and ears open for anything strange,’’ 27-year-old Charlotte Kimbrell, of Belleville, Illinois, said before a screening of “Dark Knight’’ at a theater in nearby O’Fallon. “I’ll probably be sitting all the way in back today, away from the exit doors.’’

It was in the back of some baseball fans’ minds Friday, as well.

“I think paranoia takes over after something like that and something like today, but I think for the most part, all they can do is check your bags and hope that you’re not crazy,’’ said David Karney, of Quincy, Michigan, who watched the Detroit Tigers host the Chicago White Sox. “At the end of the day, if you’re crazy and want to do something, you’re going to do it.’’

The angst is understandable after the attack, which was one of the deadliest mass shootings in recent U.S. history. But security experts say changes made at ballparks, theaters and concert venues after the Sept. 11, 2001, terrorist attacks have gone a long way toward making them safer.

“The problem is security is never 100 percent,’’ said Richard Sem, a longtime security management executive from Wisconsin who is now a consultant. “We look at what’s reasonable, practical. You don’t necessarily need Fort Knox to go to a Sunday afternoon baseball game.’’

A decade after the terrorist attacks, at ballparks and concerts, bag checks are now common when entering a venue. Sometimes, there are metal detector wand scans at sporting events. Some movie theaters already have random bag checks. But experts say that it can be a difficult choice to decide where to install additional extra measures, and note that it’s no guarantee a patron will be safer with them in place.