Offer your thoughts or opinion on the input financial query or topic using your financial background.

Why are there hidden bids and offers in the US stock market for the more illiquid stocks?
When you place a bid between the bid/ask spread, that means you are raising the bid (or lowering the ask, if you are selling). The NBBO (national best bid and offer) is now changed because of your action, and yes, certain kinds of orders may be set to react to that (a higher bid or lower ask triggering them), also many algorithms (that haven't already queued an order simply waiting for a trigger, like in a stop limit) read the bid and ask and are programmed to then place an order at that point.