I notice quite often on a footprint chart (let's say one minute footprint chart) that there is a significant number of contracts traded at a certain price without price moving-here I am talking about FX futures in particular. Quite often (a few times a day at least), this amount of contracts trades in a single second. Say, today, around 11:24am about 500 contracts hit the bid at 1.2735 in 6E within a single second(!) and the price didn't move. Clearly there was hidden liquidity at the level. I am seeing this day by day in various FX futures. Is it just arbitrageurs sitting on prices arbing vs spot FX that provide this liquidity? I am trying to figure out if someone has a clue as to the origin of this type of liquidity.