In this animation, towards the end (about three quarters) the process of transcription termination is shown. It states that the transcribed RNA forms a hairpin loop (or stem-loop), which halts the transcription process.
My question is, why does it halt the transcription process, considering that the RNA polymerase moves in the opposite direction of where the stem loop is created? Does it somehow change the RNA conformation such that no further bases can be added? Interpreting it as a physical obstacle doesn't seem to make any sense here.