Answer:
Plasmodial slime mold
Explanation:
The description given above in the question most likely points to that of Plasmodial slime mold. Plasmodial slime mold, which is usually yellow in color, is formed by flagellated cells that swarm and merge together, forming a large, multinucleated single cell. This multinucleated single cell with a large cytoplasm have many nuclei. This slimy multinucleated single cell take the appearance of a slimy webwork structure and is commonly found on decaying logs.
The organism found growing on a decaying branch, while walking in the wood, is most likely a plasmodial slime mold.