Great Game....
...but I would like to offer some suggestions to help polish it up a little.
1. Tie the Replay and Start options to the space bar, when I lose I hate having to reach for the mouse each time I want to try again.
2. Have a practice mode which lets to practice levels you have reached in normal play without having the step though all the basic levels first.
3. Let me kill two cavemen at once.
I have to say the as 'frustrating' as the game can be, it does give you that sense of accomplishment that most flash games fail to provide. I am still struggling to get past the 2nd wind stage, but will keep on trying.