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Today I learned:

Hahajima Island of Japan is home to a fragile snail. All right, “fragile” in the sense that it is really tiny—around 0.25 centimeters (0.1 in). A thumb can easily crush Tornatellides boeningi.

When researchers recently collected bird feces on the island, they found that it contained snail shells. Oddly, some of the snails appeared to be alive. Curious, the team fed over 100 mollusks to a captive population of the two bird species known to snack on the snails.

Remarkably, around 15 percent were expelled unharmed. One snail even gave birth shortly after being pooped out. The digestive system is not a Disney ride. The snails endure a harsh journey lasting 30 minutes to two hours. Why such a good percentage appear to suffer no ill effect is a mystery.[1]

The best theories at this point?

Small equals survival. Tinier shells might be less prone to cracks and digestive juices seeping in. Tornatellides could also seal themselves away behind a mucous film that safeguards the shell’s opening.

From here. Yeah, Wiki, it ain't.