Shout Out / Crash Course

• In one video, Hank mentions himself and his brother discussing who their favorite Doctor Who is (Tom Baker and David Tennant respectively) which immediately caused fans to point out the character's name is actually The Doctor.
• In one episode there was a Tardis shown, and the caption read: "You're welcome Whovians."
• In one Psychology episode, mention is made of the thoughts going through your head as you're suddenly woken up, such as whether or not Weeping Angels are real.
• In another video, John says that, just like Voldemort's soul, he's gonna break the video into eight parts.
• A sticker on John's laptop reads "This machine kills fascists".
• "Fighting over such things, like whether the proverbial cake is a lie rarely accomplishes anything."
• In the episode about Japanese History, the Thought Bubble had Amaterasu do a cameo.
• In another episode Thought Bubble had Solid Snake do a cameo, and in the US History episode they had Skrillex appear as a US delegate.
• Just about any mention of tortoise shells brings a Red Shell to attack John in World History, therefore overlapping with Running Gag.
  • Any Thought Bubble sequence — especially when John's reading a quotation — tends to be littered with shoutouts and pop-culture references. There are also a couple of minor recurring characters that appear throughout the ages in World History.
• A particularly clear one in Psychology: "Measuring Personality" opens with a lineup of people who are fairly obviously Bennett, Morello, Crazy Eyes, Red, Norma, and Taystee.
• US History video number 6 contains a "Libertage" (liberty montage) captioned with "America: making the Kessel Run in less than twelve parsecs since 1776."
• The CC Games episode on PC gaming opens with Andrew giving a shout out to the "PC master race"—a term coined back in 2008 by Zero Punctuation.
• Episode 15 of Psychology has a Super Mario Bros. reference in the form of a chibi Hank hitting Brick Blocks and getting an Anglerfish suit as a powerup from an invisible block.
• Episode 16 of Psych has a brief moment where a guy playing DanceDanceRevolution appears on the side.
• E.T. the Extra-Terrestrial and a Pokéball appear in Episode 19 of Psych.
• Rorschach, Kratos, Superman and Count von Count appear in episode 21 of Psych.
• Ash Ketchum makes a few appearances in Episode 25 of Psych.
• Episode 34 of Psychology contains quite a few references, including a transformed Delorean, a passing reference to Bambi, and cameos from Neo, Ted, Miley Cyrus, Walter White, and the Angry Sun.
• Starting at Episode 12 of Philosophy, in the new Squarespace sponsor there's a person waving a sign. If paused at the right moment, behind them, Sherlock Holmes can be spotted in the crowd.
• Frequently, speeches about railways will include a character holding Thomas.
• In the episode on Langston Hughes and the Harlem Renaissance, the very first Thought Bubble annotation on a historical monologue/writing features several class symbols from Team Fortress 2.