Throwing It All Away - S10-E15
Factual error: In the opening scenes, Arizona mistakenly says a child suffering from imminent liver failure is at risk for psoriasis, when the script called for the word cirrhosis. Psoriasis is a skin disease. Cirrhosis is the medical term for end stage liver disease.
The Beautiful Day in the Neighborhood - S5-E4
Factual error: Near the end, the gang is using Luminol to check for blood on neighbourhood signs. Luminol won't work in broad daylight, they should have used a blue light filtering lens to enhance its visibility.
How I Met Everyone Else - S3-E5
Factual error: When Ted is talking about what Marshall told him after he met Lilly, the two boys are playing with Playstation 2 controllers. The scene takes place in 1996, and Playstation 2 didn't come out until 2000.
Factual error: The verse Octavia recites is from Virgilius' poem "the Aeneid". That poem was written at least a quarter of a decade after the death of Caesar.