I am sure a naive question, but can someone explain what is...

I am sure a naive question, but can someone explain what is happening with the many trades of less than about 5 shares that occur with some stocks?
For example, on Tuesday I watched ERA go from a low of 19.86 to a high of 21.39 with many of these small trades appearing (I can only see Commsec's course of sales) to create ever new highs and then a large trade comes through. And of course today it's working in reverse with the price going down.
Am I correct in guessing that there is an automated program watching the stock and using an algorithm relating price, volume, depth etc and making the required trades?

Of course I am not suggesting any ulterior motives in any of this....