Today you can learn a new phrase: ‘turn to jelly’. If you turn to jelly, it really means you suddenly feel very weak because you are nervous or frightened. Sometimes you can say your legs or another part of your body turns to jelly and this means the same thing.
When I saw how high up we were, I turned to jelly and I couldn’t speak.
His legs turned to jelly after riding the ghost train at the funfair!