It’s the Balsa and Cork Double Stack from A Bird Toy.
This toy is really big. By cutting it in half, I was able to put one half in with the girls and one half with the boys. It wasn’t long before the girls started nibbling. The top balsa block was almost gone an hour later.
The balsa block has not yet been devised that could go 12 rounds with Sunny. Look at that determination-face.
They must have beaver genes. Chew, chew, chew!