The Flash wasn't the only Arrowverse show to hold a "mini crossover" tonight.
Spoilers for tonight's episode of Legends of Tomorrow, 'Return of the Mack', below.
The episode saw the Legends investigating a string of vampire attacks in 1897. They discover a watch from the present day with mysterious sets of fingerprints - one of which belongs to Arrow's Oliver Queen (Stephen Amell).
Ray Palmer/The Atom (Brandon Routh) and Jax Jackson/Firestorm (Franz Drameh) panic, and decide to contact Team Arrow to warn them. They reach Curtis Holt/Mr. Terrific (Echo Kellum), and explain the problem to him over video chat.
In the grand scope of things, this crossover has pretty small bearing on the Arrowverse's plot. (The topic they're talking about, however, could very well be a different story.) But it isn't the first of its kind in this season of Legends, with The Flash's Kid Flash/Wally West (Keiynan Lonsdale) appearing alongside Nate Heywood/Steel (Nick Zano) in the season three premiere. And overall, it does hint at the Arrowverse growing into an even closer web - something that will be seen in action in this year's 'Crisis on Earth-X' crossover.
"I'm excited about all of that." Legends star Victor Garber revealed earlier this year. "As exhausting as all of that is [crossing the shows over], and very disruptive to schedules – because everybody's trying to figure out how they're going to shoot their episode that week – it turned out to be a lot of fun."
Legends of Tomorrow airs Tuesdays at 9/8c on The CW.