This article contains spoilers for The Flash season 5 episode 8.

For my money, the absolute most chilling part of The Flash‘s 100th episode, “What’s Past is Prologue,” was the relatively quiet scene between Eobard Thawne’s Wells and a Season 1 Cisco.

In the space of one scene, we get a painful reminder of just how dangerous Thawne is as the episode calls back to one of the Season 1 scenes that doesn’t make it into this walk down memory lane: That time Thawne put his hand through a heartbroken Cisco’s chest. It does more to make us downright terrfied of what Thawne could do moving forward than any explicit threat could.

Den of Geek had a chance to talk with Tom Cavanagh (Wells/Thawne), who also directed the episode, as well as Carlos Valdes (Cisco) about what it was like filming this all-important scene.