"They ask great questions, and they're bright guys," O'Brien said. "They're really fun to coach."
Hackenberg, a 6-foot-4, 220-pound, five-star recruit, has had fans drooling over his potential since he committed in February. The 6-3, 213-pound Ferguson has sophomore eligibility after breaking multiple school passing records at the College of the Sequoias last year.
O'Brien made it clear that whoever starts Week 1 is not necessarily the starter for the rest of the season.
The second-year coach said that he believes in playing one quarterback, but that it's more likely the two signal-callers will both get opportunities.
"We haven't ruled out anything," O'Brien said.
Because of NCAA sanctions and a large graduating class from last season, Penn State will enter the 2013 season with just 65 scholarship players. That makes it all the more important for players to avoid injuries.
O'Brien described his team's overall health Thursday as "decent."
Linebacker Ben Kline, who had offseason shoulder surgery, was day-to-day, the coach said, but he is expected to be ready for Week 1.
Freshman receiver DaSean Hamilton is done for the season with a lingering wrist injury, and sophomore tight end Brent Wilkerson is out for "a while" with a back injury.
Considering Wilkerson's status, O'Brien said freshman tight end Adam Breneman, a high school all-American, will definitely play this year. Breneman will battle for playing time with sophomores Kyle Carter and Jesse James and senior Matt Lehman.
Hull continuing Linebacker U.
The Nittany Lions will have to be particularly careful at linebacker, where an injury would be a massive blow. Penn State's three starters - Glenn Carson, Mike Hull, and Nyeem Wartman - are expected to fill the void left by NFL draft picks Gerald Hodges and Michael Mauti. The talent is there, but the depth is missing.
O'Brien spoke highly of Hull, who made 58 tackles and had four sacks coming off the bench last season. The senior has been doing just about everything right in camp.
"He's a guy that means a lot to our football team," the coach said.
O'Brien made sure to note that Lehman and receiver Brandon Felder both graduated in Penn State's summer commencement ceremonies last weekend.
"Make sure we put that in your articles," O'Brien jokingly told reporters.
That brings Penn State's number of players seeking graduate degrees to eight.
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