They then, on the Twits' return, have two birds drop some glue onto the couple's heads. Upon entering their house, the Twits presume that their living room has turned upside down and that they must therefore be standing on the ceiling, so they stand on their heads and become stuck.
Upon the Twits' return, two birds put some glue on the couple's heads. When the Twits enter their house, they think their living room is upside down and assume they are standing on the ceiling, so they stand on their heads and get stuck.