Question: What season had a gag reel?
About the article "The Big Bang Theory", section "DVD/Blu-ray releases".

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The DVD release of season two was released by Warner Bros. in the US on August 23, 2005 after it had completed broadcast on television.
As well as every episode from the season, the DVD release features bonus material including a gag reel, audio commentary and a fashion featurette.
: - In the UK the DVD was released as a 6-disc set.
Omitted was the US release seventh disc that featured Beachy Couture, Obsess Completely and the two season gag reel.  
  Season 1 extras Four disc set Two Adults, One Kid, No Grown-Ups – behind the scenes with the cast and crew.
Backstage tour with Angus T. Jones.
Dolby Stereo 2.0 sound format Gag reel.
Season 2 extras Four disc set 2 Days in the Life of 2 – viewers are invited for a behind-the-scenes look at a typical day in the life of cast members Charlie Sheen, Jon Cryer, and Angus T. Jones.
The Serious Business of Writing Comedy – a hilarious look at what it really takes to write a comedy show.
Dolby Stereo 2.0 sound format Gag reel.
Season 3 extras Four disc set Dolby Stereo 2.0 sound format Gag reel.
Season 4 extras Four disc set Two men talking about Two and a Half Men – Creators Chuck Lorre and Lee Aronsohn talk about the show.
"Tucked, Taped and Gorgeous" commentary with Chuck Lorre and Lee Aronsohn.
"Mr. McGlue's Feedbag" commentary with Charlie Sheen, Jon Cryer, and Angus T. Jones.
Dolby Stereo 2.0 sound format Gag reel.
Season 5 extras Three disc set "Two and a Half Men" at 100 – featurette on the show's 100th episode.
The Lore of Chuck Lorre: Must Pause TV – the genesis and evolution of his vanity cards at the end of each episode.
Dying Is Easy, Comedy Is Hard – chronicling the crossover episodes between writing teams of "Two and a Half Men" and "CSI: Crime Scene Investigation".
Bonus episode: "CSI: Crime Scene Investigation" – "Two and a Half Deaths."
Dolby Stereo 2.0 sound format  Season 6 extras Four disc set Growing Up Harper – The evolution of Jake Harper and the actor who portrays him, Angus T. Jones The Women of "Two and a Half Men" – Interviews with the women Dolby Stereo 2.0 sound format Gag reel  Season 7 extras Three disc set Ghosts of Charlie's Girlfriends Past Featurette Dolby Stereo 2.0 sound format Gag Reel  Season 8 extras Two disc set Dolby Surround 5.1 sound format  Season 9 Extras Three disc set 2.5 Men, Version 2.0: Experience the excitement of the first night Ashton Kutcher took the stage, through backstage footage, crew, audience and talent interviews.
The Billionaire Upgrade – Walden Schmidt’s Malibu House Redesign: The Harper House is due for a makeover when Walden Schmidt snaps it up, and it’s up to the crack production design team at "Two and a Half Men" to express Walden’s personality in a big overhaul of the show’s signature set.
Dolby Surround 5.1 sound format Gag reel  Season 10 Extras Three disc set Two Manly Men Singing and Dancing – Ashton Kutcher and Jon Cryer take us behind the scenes in the production of their first-ever musical number.
Dolby Surround 5.1 sound format Gag Reel  
The first season of the American sitcom "The Big Bang Theory" was originally aired on CBS from September 24, 2007 to May 19, 2008, over 17 episodes.
An unaired pilot also exists.
The Season 1 DVD came without a gag reel and is, so far, the only "Big Bang Theory" DVD set not to have one.
The reissued Blu-ray, was released July 10, 2012, and includes a gag reel that is exclusive to the set.
The episodes on Blu-ray are all in remastered surround sound, whereas the DVD version had stereo. 
"Psych: The Complete Eighth Season", consisting of ten episodes, will be released on April 1, 2014.
The three-disc set includes deleted scenes, episode podcasts, and a gag reel.
The seventh season television special "" is also included. 
"The Glades: Season One" was released on DVD in region 1 on June 14, 2011, and region 4 on March 7, 2012.
It contains all thirteen episodes of season one.
Special features include, Deleted scenes, Gag reel, Behind-the-scenes footage, "Sunshine State of Mind: Casting The Glades" and "A Location for Murder: Filming in The Glades" featurettes and Cast commentaries.
"The Glades: Season Two" was released on DVD in region 1 on July 10, 2012, and is set to be released in region 4 on February 27, 2013.
It contains all thirteen episodes of season two.
Special features include, Deleted scenes, Commentary, "Jim Longworth's Guide to Police Work" and "Love Triangles: Relationship Complexities and The Glades" featurettes and Gag reel.