The Professor sees the arrival of a homing pigeon on the island as an opportunity to be rescued, and immediately begins to feed it a special diet designed to strengthen it so that it can fly again. In an attempt to speed the recovery time, the other Castaways also feed the pigeon, causing it to become too fat to fly. The pigeon is also trapped for a short while in a cave by a ""deadly six-foot black morning spider."" (thetvdb.com)