Foxwoods rules re: showing cards HU

[Ghazban]

I was talking to an acquaintance at Foxwoods over the weekend who said that, in a HU pot, he went allin (1/2 NL game) on the flop and the opponent was considering a call. My acquaintance then flipped his cards over to show he'd flopped a small flush (I guess he wanted the other guy to fold a naked A rather than call and possibly run him down). Is this legal there? I thought I'd heard that showing cards during a hand was not permitted in either cash games or tournament games at Foxwoods but I wanted to double check. Thanks in advance.