This article contains plot details from the latest book.
Squelchberries are a common Elvin remedy. They contain the nutrients of an entire meal in one bite, and therefore can help the recovery of people who haven't eaten for a while. However, their sticky juice can glue the jaw shut if too many are consumed at once.
In Unlocked, the Physician Elwin Heslege gave Keefe Sencen squelchberries after Keefe woke up from his few-days-long coma. But Keefe consumed three berries at once and glued his stuck jaw, needing to drink some bottles of Youth to get free.