This remind me of San-nakiji... The act of eating a baby octopus alive... Which sometimes could resulting in death from the octopus putting it's tentacle into your trachea or stuck it self on your throat, effectively blocking your breathing....
Also, this is the first time I think we've seen Sylphin take the lead in the "eating bravery" department, and on a food that's as unorthodox as live slimes. Good on her.
That said, eating( or drinking in this case ) living creatures "whole" to have them wiggle around inside of you is pretty messed up.
It's one thing to kill creatures to eat them, it's a whole other level to torture creatures to death with stomach acid just for the jollies of feeling them wiggle around.
This is different from just eating shellfish so fresh that their muscles haven't quite died and are still writhing. These slimes are straight up alive, from the start all the way to when they are in your stomach. And they have big eyes. And they have severe reactions to being prepared and eaten akin to being tortured.
As much as I want to call the dude a coward, I don't think I'd have the guts myself.