Which of the following is NOT a definite indicator of decay?

A fruiting structure, such as mushrooms or conks, is commonly associated with decaying wood, as they are produced by fungi that break down organic material. These structures serve as a clear sign of decay because they indicate that the tree is hosting fungal activity that typically leads to the degradation of tissues.

The other options represent potential indicators of decay as well. A cavity signifies internal decayed wood, where the integrity of the tree is compromised. A nesting hole, while it may not directly imply decay, often indicates that the tree has some level of hollowing, which can be a result of decay processes. Oozing can suggest internal rot or other issues resulting in sap leakage, further indicating decayed conditions.

In this context, the fruiting structure stands out as a distinct indicator of fungal decay, while the other options can sometimes correlate with decay but do not specifically indicate it directly.