Update training-slides/src/deconstructing-send-arc-mutex.md

Co-authored-by: Jonathan Pallant <[email protected]>

training-slides/src/deconstructing-send-arc-mutex.md

@@ -55,7 +55,7 @@ Two allowable options:
 * applies to data passed from parent thread to child thread or vice-versa
 * prevents passing references to local variables
   * one thread can finish before the other and such references may become invalid
-  * `+ 'static` lets borrow checker detect these situations at compile time
+  * `+ 'static` avoids this by ensuring any references point to data that has the static lifetime (i.e. that lives forever)
 
 ## `T: Send`