It might be hard to see, but this is one snail riding another snail's shell as they both hang upside down from the top of snail-opolis.
The snails were extracted from their environment while L cleaned and redesigned their home. Our current snail count is 11. This suggests a few have made successful escape attempts, probably when they were so tiny that it was difficult to seal off their habitat. Or, less likely, snail cannibalism.