These tabby cabins were built up in layers. The holes were made by logs that bound the two sides of the forms into which the tabby was poured. As this technique was labor intensive, that was in large part due to what went into the manufacture of the tabby, and the layering and drying process of building with it.
Thanks, John. And, I'm happy to dispel any concern that cats and kittens have any part in tabby. But, if you're an oyster, expect to be forever entombed in a slave cabin reconstruction.