Vegan Seltzer Rage

Last night at dinner Ryan gave a very hard look at the can of seltzer that he was drinking.  Looked, then proclaimed "I'm never drinking this ever again!"

Me: Why???

R (emphatically): It is vegan!

Me: Ryan, what animal product do you think they should put in seltzer???

Ryan: pause... “Oh, I thought it meant something else.  Then I guess it is OK.”

I have no idea where that came from or what he thought it meant!