  Not every particle that forms a nematic liquid crystal makes a smectic. The
particle tip is critical for this behaviour. Ellipsoids do not make a smectic,
but sphero-cylinders do. Similarly, only those N-CB alkylcyanobiphenyls with
sufficiently long ($N\ge 8$ carbons) alkane tails form smectics. We understand
the role of the particle tip in the smectic transition by means of a simple
two-dimensional model. We model sphero-cylinders by "boubas" with rounded tips,
and ellipsoids by "kikis" with pointed tips. The N-CB molecules are modelled by
a small body with a polymer tail. We find that rounded tips and longer polymer
tails lead to a smectic at lower densities by making the space between layers
less accessible, destabilizing the nematic.
