One of the biggest surprises in Spider-Man: Into the Spider-Verse was how terrifying they made Prowler (voiced by Mahershala Ali). He looks scary as it is, but thanks to great character design and the use of an audio cue, he instantly became one of Spider-Man’s best big screen foes.

Turns out, the sound used to telegraph Prowler’s presence was an elephant through a filter, according to Into the Spider-Verse co-director Bob Persichetti, who spoke to io9.

That came from our amazing composer Daniel Pemberton and… it’s an elephant. Weirdly enough an elephant through a filter and it’s really just became his siren. It’s really unnerving and disturbing.

We used to have a song in there that had, not that exact sound but something that had the same expressive quality as that, and it was the beginning of a song. It was a mixed song and we just played that over and over and he turned it into something much more organic. It’s really haunting, man.

The work done by Pemberton truly makes Prowler an all-time villain. He genuinely seemed dangerous.

If you don’t know what Prowler’s cue sounds like, check out his theme below.

Spider-Man: Into the Spider-Verse is in theaters now.