Yes, you can! This is enabled by the setting live preview. This setting enables you to see what your visitor is typing in real time. Please note that the visitors do not know this. Therefore it's important not to start typing or send your answer before the visitor has sent his och her message.

To activate/deactivate this feature, go to Settings via your profile picture in the lower left corner. Go to Messages and Display options. For the feature to be active, the box Enable live-preview has to be ticked.