  The Gaia snail is a spiral feature in the distribution of solar-neighbourhood
stars in position and velocity normal to the Galactic midplane. The snail
probably arises from phase mixing of gravitational disturbances that perturbed
the disc in the distant past. The most common hypothesis is that the strongest
disturbance resulted from a passage of the Sagittarius dwarf galaxy close to
the solar neighbourhood. In this paper we investigate the alternative
hypothesis that the snail is created by many small disturbances rather than one
large one, that is, by Gaussian noise in the gravitational potential. Probably
most of this noise is due to substructures in the dark-matter halo. We show
that this hypothesis naturally reproduces most of the properties of the snail.
In particular it predicts correctly, with no free parameters, that the apparent
age of the snail will be $ \sim 0.5$ Gyr. An important ingredient of this model
is that any snail-like feature in the solar neighbourhood, whatever its cause,
is erased by scattering from giant molecular clouds or other small-scale
structure on a time-scale $\lesssim 1$ Gyr.
