Three months after returning from Belize, Vanessa of NatureBreak.org felt and heard the activity of a botfly larva in her scalp (I can recall reading an article in BBC Nature magazine about a cameraman who suffered this - he reckoned it was scritching against his skull!).
Botfly larvae are bulb-shaped, the the posterior spiracles poking out through a small hole in the skin - the main body of the larva is covered in backward pointing spines which serve to prevent the larva from being removed.
Being somewhat more enterprising and courageous than I probably would have been (despite my being a "trained entomologist"), she recorded the removal of said larva and posted it on YouTube.