  Star colloids are rigid particles with long and slender arms connected to a
central core. We show numerically that the colloid shapes control the rheology
of their suspensions. In particular, colloids with curved arms and hooks can
entangle with neighbor particles and form large clusters that can sustain high
stresses. When a large cluster permeates the whole system the viscosity
increases many fold. Contrary to the case of spherical colloids we observe that
these effects are very strong even at moderate volumes fraction over a wide
range of P\'eclet numbers.
