What is this hole on my stairs?

[Intothevalley]

Just pulling up the carpet in our new house to assess the state of the stairs, and the bottom step has this round hole (about 2cm diameter). My first thought was MOUSE but the carpet was tightly laid and the underlay and carpet didn't have a hole, or any gaps...

The other black marks which might look like holes are staples with underlay attached.

It’s a hole. Made by a human with a tool, not by a rodent or an insect

These are the exact words I wanted to hear - I imagine they made it for ventilation, or to tighten a screw under the stairs or something.

Thank you!

Bad DIY? Probably a cable was through it at some point.

Looks like a cable came through at some point. We have that for our car charger

Thanks folks! A cable makes sense - there's a socket under the stairs, and the kitchen was recently extended, so I imagine they needed power for that.