  It has long been believed that swimming eukaryotes feel solid boundaries
through direct ciliary contact. Specifically, based on observations of behavior
of green alga Chlamydomonas reinhardtii it has been reported that it is their
"flagella [that] prevent the cell body from touching the surface" [Kantsler et
al. PNAS, 2013]. Here, via investigation of a model swimmer whose flow field
closely resembles that of C. reinhardtii, we show that the scattering from a
wall can be purely hydrodynamic and that no mechanical/flagellar force is
needed for sensing and escaping the boundary.
