The two low resistance n transistors at {TAIL ~ the same time} connect {HEAD ~ the data lines} to ground 
The two low resistance n transistors at { TAIL ~ the same time } connect { HEAD ~ the data lines } to ground
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH