Jwoo111,generated by I understand that these may be generated by...

Jwoo111,generated by
I understand that these may be generated by "algorithms" based on some customised logic that someone has developed. Specifically those low value $7 and $42 trades you see.
Traders set these up to run, generating buy/sell, sell/buy, black box trades, they can cause a momentum for saying selling and then all their sell bids are adjusted or suddenly cancelled and they replace them with buy.

IMO they cause false belief in what the market sentiment may really be. Institutional investors utilise these tools for their trading, some set to also react to electronic news reports or key market words instantaneously for a particular stock type. Again the above is my lay-man understanding and welcome clarification from those more informed.