This is actually "self-seasoning" of clams that is often done prior to cooking. It's actually not eating the salt, but is searching for a new home with its foot (not a tongue). The rapid retraction when it touches the sand may indicate severe pain.
Urine at least could go down fast even if it didn't taste good
Poop you'd have to chew if it is solid and it stinks and it will leave a vomit-inducing taste in your mouth until it goes away. No contest poop is worse 100%