What are these?

[RUNNERBUN]

What are these? I found the first one in the water jacket at the rear end of an engine block, which had the head removed when I found it and consequently did not pay to much attention to it as I thought that somehow it got in there by accident. However, some time later I removed the head off another engine and found the second one. It was only then that I realised that these stars were in there from original manufacture of the blocks. Both were found in approximately the same location within the water jacket at the rear of the blocks.
I am assuming that they must have been part of the manufacturing process in the casting of the blocks. Their location in the rear of the block certainly did not help in the circulation of water to the rear of the block.
Has anyone seen these items before or maybe shed some light on the subject.