I have noticed this behavior many times with Black Rat snakes as well, with same sexes and with opposite. Freshly caught Blacks will flick their tongues at each other and twitch, almost like they are checking each other out like a dog might. After observing this many times over the years, I think it is a form of communication, they are having some sort of basic conversation as you might call it- because I've seen it happen outside of the breeding season quite a bit.
-----
1.1 Newton County Indiana Bulls
1.0 Texas Redish Bull
0.1 Kansas Yellow Bull
2.2 Red X Yellow Bull
1.0 Medicine Hat Alberta Canada Bull
1.2 Ball Pythons
1.2 Coastal Chocolate Cal Kings
1.0 Banded Desert Cal King
0.1 Gray Banded King
0.1 Jasper County SC Corn
1.2 Henderson County NC Black Rats
0.1 South Carolina Northern Pine