All three of them are ladies, so they can’t. At least not visibly.
Once when we were just playing around with clicker training (101 things to do with a clicker and a popcorn tin), I clicked my Zoe girl as she was stepping over the popcorn tin. It was right as her back paw touched the top of the tin. [click!] She was right back there trying to get the click again (tap, tap, tapping with the hind leg) and it didn’t take long before we had the behavior on the cue “boy dog” and the popcorn tin faded down to one of those little dancing flowers. Then we’d ask, “Zoe, what’s the difference between a girl dog and a _boy dog_?”” and she’d raise her hind leg...
We also were able to get her to yawn on cue.
Wish we would have videotaped that stuff. :-(