Chosen answer: The CIA placed Klaus' brain inside a goldfish. The reason the CIA did this was because Klaus was once an Olympic ski-jumper and was supporting East Germany in the 1986 Winter Olympics. The CIA knew Klaus was going to win the gold medal for ski-jump and they did not want this to happen, so the only alternative they could think of was to place Klaus' brain inside the body of a goldfish before he could compete.
Chosen answer: Toph had Katara use it to send a letter to her parents. It never returned.