Reminds of this post of someone who added a camera to the little cat door because the cat kept bringing 'gifts' (mice) indoors. He used ML to detect if the cat brought a gift. In that case he temporarily locked it.
Not sure if it is the same project, but I remember something like that from a long time ago. The cat would walk through a backlit tunnel and project a black and white silhouette of its profile onto a low res camera.
They used a very simple neural network to do the detection. Several example pictures were included in the write up, showing the cat normally, one where it was holding a mouse, as well as a profile of a possum (IIRC).
Replicating those results has been on my to-do list for over a decade.