Hi, Harrie and all. I've found now and then that even a shell that
I 'thought' the animal was out of, actually had a little left, deep
inside, as much as a month or so after bringing it home. I've
found and following suggestions from others, that soaking the shell
for several days in clean water ( change it every now and then)
loosens things up. To finalize the job, I hold the shell under a
high pressure faucet (luckily have that in my basement). Voila -
EVERYTHING out.  And then it smells like a rose.

I find pine oil is great for big shells, but avoid it with the
small ones- seems to be an 'operculum eater'.  But the great thing
about pine oil is you only need a teeny bit to do the job.

Karen