It’s been known since at least 1998 that if you obscure someone’s arm from them visually, show them a rubber replica, and gently stroke their real arm and the replica in synch, they will identify the replica as part of their body, and react defensively to apparent harm to it.

This has been reproduced in other mammals — but now it turns out that octopuses will also react the same way:

https://www.science.org/content/article/octopuses-fall-rubber-arm-illusion-just-us