Comment on "Inflation with a graceful exit and entrance driven by
  Hawking radiation"
  Modak and Singleton [Phys. Rev. D 86, 123515 (2012)] have presented
Hawking-like radiation for cosmological inflation which has a natural "turn on"
and a natural "turn off" mechanism. This Hawking-like radiation results in an
effective negative pressure "fluid" which leads to a rapid period of expansion
in the very early Universe. We discuss that the turn on mechanism can not
happen for FRW model in early universe because its horizon is apparent horizon
not event horizon. Hence, we cannot apply geometric optic approximation which
is a necessary condition for tunneling method. It was shown that this model
predict a value for $\frac{\rho}{m_{pl}^4}$ which is bigger than the COBE
normalization constraint in the Cosmic Microwave Background (CMB) at the
horizon exit.
