A good exercise for exploring and extending the vocal range.  It will help to eradicate unexpected 'catches' in the throat from occurring when speaking or singing.   It's also a very good icebreaker.

• Take a deep breath and make an ‘ooh’ sound.  Keep this soft to avoid straining the vocal cords.
• Move this sound upwards until you reach the top of your vocal range, then come down to the bottom of your range.  From here, turn and move back up towards the top again.
• Continue up and down through your range, breathing when you reach the end of each breath and restarting from where you left off.  ‘Massage’ with sound any parts where the voice disappears, or is broken, by singing up and down through that area of your range until the voice returns.

Note: be careful not to hyperventilate and sit down and rest if you begin to feel dizzy.  

This activity is taken from Adventures in Sound, available as an e-book.