Like Aubrey said, they can be popped but palpating is much easier.
To palpate, hold onto the snake with one hand pre-vent and belly up. (once you get the hang of it you can do belly down just as easily)
Place thumb along spine and KEEP it there.
Start with fingertip at vent with mild preasure slide fingertip toward tail. Somewhere around 6 - 12 scales (or something like that) if it's a male you will feel one or two little bumps slip under your fingetip.
Check several until you find a male, or if you have a known male even better. You will NOT always feel the bump and may have to reposition your finger to one side or another. And some are, shall we say, more blessed with hardware than others.
Once you find the BB's on any individual you are done, it's a male. I usually re-check my "females" at a later date to see if any bumps now show up.
Here's the gif showing me palpating a young BCI, same process for BRB's, just a little smaller.

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Thanks,
Dave Colling

www.rainbows-r-us-reptiles.com
0.1 Wife (WC and still very fiesty)
0.2 kids (CBB, a big part of our selective breeding program)
LOL, to many snakes to list, last count:
26.49 BRB
20.21 BCI
And those are only the breeders 
lots.lots.lots feeder mice and rats 

