Some interviewees, through a mixture of over-enthusiasm and inexperience interrupt their interviewer when they are mid-sentence, which is a huge no-no in interviews.
Even if you feel what you must say is very important and of huge significance, take a deep breath, bite your tongue and wait until your interviewer is finished talking. If you do not understand the question being asked, again wait for your interviewer to finish talking and then ask for clarification when they are fully completed talking.
Put yourself in your interviewer’s shoes when they are being interrupted mid-sentence. You will quickly realise from their perspective that the interviewee is perceived as being disrespectful or plain rude.
Of course, this rule not only applies to face to face interview but also to phone and Skype interviews. When an interviewer is speaking, they generally feel that the information they are imparting is very important and demands their complete attention. Consequently, cutting off your interviewer mid-sentence could be hugely detrimental to you landing the position on offer.