Another couple of points to remember when interviewing is to stop speaking as soon as you ask a question, let the interviewee answer, but resist all attempts at umming and aaahing or talking over them like we do in everyday conversation, just nod your head in agreement. It will make editing (shortening) a long winded response to a question much easier. Also, don't tell the interviewee exactly what questions you are going to ask them, just give them a general idea of the areas you will be covering, so they don't dry up in front of the camera, or is it called Corpsing? I don't know how much work you want to take on but here's a suggestion for your grandparents reminiscing, you could have a shot of them in the local park, then use a defocus fade and use two children in sepia to play the part of them when they were that age, you can just let them run around in their 2006 clothes.

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Better than a poke in the eye with a pointy stick any day...