Each song, on Wednesday, was translated into a different language and then back to English, resulting in completely different lyrics.
Halsey performed "Like a Virgin" by Madonna which became "Unwed Woman."
"Unwed woman/ For the first time explored outdoors/ Unwed woman/ When your chest hurts they're nearby," Halsey sang using the new translated lyrics.
Fallon performed "ABC" by the Jackson 5 which became "Alphabet" and Halsey performed her song "Without Me" which turned into "You Soft Head."
The pair then came together for a duet of "I Want It That Way" by The Backstreet Boys which became "I Desire Roads."
"I haven't ever said whoops/ Say because/ You have failed in hearing/ I desire roads," Halsey and Fallon sang.
Halsey also used her New Jersey accent to recite the lyrics to her song "Graveyard" and competed against Fallon in a portrait-drawing contest.