They usually use drinks or eat snacks to make certain sounds. Including sucking their own hands. Its actually fcking wild lol.
really??? XDXD. that's so hilarious
as anon stated. sometimes water. or with their mouth/lips. sometimes, the producers record a separate sound and combine it.
and nah, it's part of professionalism to not react to it, or at least hide your embarrassment. they are paid to record smut with a straight face after all. at least not to make it obvious in the voice. there are some seiyuu that are pretty much used to it no matter if the line is racy or cringey . it's like acting but with a voice.
When I listen to BLCDs, I keep on wondering how the seiyuu make such erotic sounds? Are they the one who made it or just technically made? Are they not embarrassed or felt awkwardness? hahaha..