There’s varying studies. Some place it around 2%, others closer to 5-8% (it varies based on gender). But I see most average out to about 3-5% (this just means the person has done it once before to some extent, even if they don’t do it often).

It also massively varies based on rural vs urban, educated vs non educated, cultural backgrounds, time period, age, geography, etc.

Wikipedia is a good place to start, as always. There’s some good sources cited within it.

But TLDR: it’s much more common than you think it is. Hence why it’s terrifying.

https://en.wikipedia.org/wiki/Zoophilia