A "Sawdust Woody" is a slang term used to describe a false erection that appears visually idyllic but is actually soft and pliable when examined. It's a "counterfeit erection" that may occur due to various factors such as anxiety, medication side effects, or medical conditions.
*Becky to a friend* Wow, Elrond really ended up having a Sawdust Woody - very disappointing.
As a saw moves back and forth through a tree, so does the penis move through the anus spraying debris. See anal shavings.
Last night when my boyfriend performed anal sex on me, my asshole underwent extreme friction causing the dreaded sawdust effect leaving flung skin and fecal matter everywhere. Damn, what a mess.