Which of these is NOT a defect found in timber planks?

The choice indicating "crushed" as a defect not typically found in timber planks is accurate because crushing generally refers to a form of damage that occurs due to excessive load or physical impact, often seen in structural materials like concrete rather than inherent flaws in timber.

Timber planks can indeed experience problems like rot, caused by fungi when they are exposed to moisture over time, leading to decomposition. Warping occurs due to changes in moisture content within the wood, resulting in deformation, and twisting can occur as a result of uneven drying or improper handling. These issues are characteristic of timber planks and can affect their structural integrity and usability. In contrast, "crushed" is not a standard defect attributed to timber itself, making it the right choice in this question.