  Astrophysical plasmas are turbulent and magnetized. The interaction between
cosmic rays (CRs) and magnetohydrodynamic (MHD) turbulence is a fundamental
astrophysical process. Based on the current understanding of MHD turbulence, we
revisit the trapping of CRs by magnetic mirrors in the context of MHD
turbulence. In compressible MHD turbulence, isotropic fast modes dominate both
trapping and gyroresonant scattering of CRs. The presence of trapping
significantly suppresses the pitch-angle scattering and the spatial diffusion
of CRs along the magnetic field. The resulting parallel diffusion coefficient
has a weaker dependence on CR energy at higher energies. In incompressible MHD
turbulence, the trapping by pseudo-Alfv\'{e}n modes dominates over the
gyroresonant scattering by anisotropic Alfv\'{e}n and pseudo-Alfv\'{e}n modes
at all pitch angles and prevents CRs from diffusion.
