[tizzdogg]

If all 261 unfoldings tile space, it makes me wonder if all arbitrary collections of 8 connected cubes do as well.

Is there an example of 8 cubes that are proven to not tile space?

[sethhovestol]

I think a ring of cubes wouldn't:

    xxx
    x x
    xxx

To fill the hole they'd need to interlock, and I think that might make it too hard to tile