That is the way PowerPoint is supposed to work. When you click the mouse in
Slide Show Mode it brings up the next item you have animated on that slide
(if you set up any). When all items are animated, the next mouse click goes
to the next slide. You can get around that by clicking "Slide Show", "set
up show" and clicking "Browsed as a KIOSK". However, ALL mouse clicks are
taken away. This way you will have to provide navigation buttons on your
slides that the person can click to go to the next slide when desired.