Similar to Douglas Adams's babelfish in that it is a small creature one inserts into one's ear. However, unlike the babelfish it affects the wearer such that they can't understand anything anyone says to them in any language even if they speak that language fluently. On a more positive note it also grants the ability to make the perfect slice of toast.
"He inserted the wibblefish into his ear and found to his astonishment that he could no longer understand his companions. From the horrified expressions on their faces he grasped that some form of danger was behind him but despite frantic..."
Quote from the book of Wibble.