Some reorg of the TTL description.

website/source/docs/agent/checks.html.markdown

@@ -31,10 +31,10 @@ There are three different kinds of checks:
  * Time to Live (TTL) - These checks retain their last known state for a given TTL.
  The state of the check must be updated periodically over the HTTP interface. If an
  external system fails to update the status within a given TTL, the check is
- set to the failed state. This mechanism is used to allow an application to
- directly report its health. For example, a healthy web app can periodically `PUT` a status
- update to the HTTP endpoint; if the app fails, the TTL will expire and the health check
- enters a critical state. This is conceptually similar to a dead man's switch.
+ set to the failed state. This mechanism, conceptually similar to a dead man's switch,
+ relies on the application to directly report its health. For example, a healthy web app
+ can periodically `PUT` a status update to the HTTP endpoint; if the app fails, the TTL will
+ expire and the health check enters a critical state.
 
 ## Check Definition