EUR/US$
AUD/US$
GOLD
SILVER
And, of course,
ES
This has been observed often in the past. The explanation could be the value of the US$, but today the DX is up a little but not that strongly. More likely the explanation is that which R.N. Elliott discussed: mass psychology. So the bears are growling at the moment, could be down hard in U.S. equity markets for a bit.