Ferder

Talking in one's sleep, usually in a nonsensical manner. It's possible to have a multiple-sentence "conversation" with someone who is "ferdering". The ferderer will not remember the conversation.

Etymology: Some English-speaking people who talk in their sleep say words that sound like "ferder ferder ferder".

"I just heard Joe talking. Is he awake?"

"Nope, he's just ferdering."