Normally you would gain 100 points each time you jump over a barrel. But try jumpin over a barrel while the following 2 conditions apply:

You are standin on the top of the MIDDLE ladder on the THIRD floor (first level)
The barrel must roll down the ladder you are on as you jump over it

If the conditions apply (as in, you jump over a barrel without movin back or forth, and it just rolls down the ladder below you), then you will hear the scorin points sound effect played multiple times really fast, and you will gain several hundred points.