Ashley (Kaitlin Olson) contracted giardia from Jess's high school boyfriend and said she saved her from a horrible river disease. However, in the episode "Thanksgiving III", Jess contracts giardia after eating a dead fish.
Ashley mentions watching the show "Ed". One of the stars of that show was Justin Long, who plays Jess's ex-boyfriend Paul.
Kaitlin Olson's appearance marks the second time an actress from Its Always Sunny In Philadelphia appears on New Girl. Mary Elizabeth Ellis who previously guest starred as Nick's ex girlfriend Caroline also has a recurring role on Its Always Sunny In Philadelphia as the Waitress.
Jess's old boyfriend that Julie Berkman's older sister "sexed" is named George Jung. George Jung was a prolific cocaine dealer in the 80's and was the main character played by Johnny Depp in the 2001 Ted Demme biopic, Blow.