Ah yes, I remember watching this; mantids will only eat live prey so keeping them as pets means you see this daily.
It's actually fascinating to me how their mouths work and I would watch them eat just to figure out their mouthparts since it seems all the tiny parts move independently to eat their prey... I'm just glad that the lack of pain receptors in a lot of their prey items means that they don't suffer as much as if they ate something with more of them such as small birds, small mice, fish, ect...
Precarious333 on youtube has some amazing high definition footage of various species doing various things; hatching, eating, threat displays, ect.