It is nothing sinister. It is real but those trades are not because people are entering orders to buy or sell 20 or 50 or 100 shares at a time. It is simply the multiple executions for larger trades. Basically the sellers brokerages software/algorithym is fighting with the buyers computer or vice versa to try to weasel each other out of a few cents.
Next time you buy or sell 1000 shares of VTSI take a look at the individual executions. Likely will be 5 to 20 executions of 20 to 50 to 100 to 500 shares at a time. The time span from first to last might be 30 seconds or a couple minutes.
News 
Market Data 
Discover 
