Summary vs. Full Body
The feed that you're publishing may have a body or a summary and a body. There's sometimes confusion about which one is which.
When using an Atom feed, there are two fields, <summary> and <content>. For Atom feeds, <summary> is always the Summary field referenced by dlvr.it, and <content> is always the Full Body.
RSS feeds will always have a <description> field, and this can be either the Summary OR the Full Body. Which one it is depends on whether your feed also has another optional field, <content:encoded>.
If your feed does not have <content:encoded>, the <description> field is treated as if it is the Full Body.
If your feed does have <content:encoded>, the <description> field is treated as the Summary, and <content:encoded> is the Full Body.
This behavior follows the recommendations set by the RSS Advisory Group.