We discuss the impact of mixing and rotation along the red-giant branch ( RGB ) on the properties of horizontal-branch ( HB ) stars with emphasis on two problems : the nature of the unexpected blue HB population in the metal-rich globular clusters ( GCs ) NGC 6388 and NGC 6441 and the cause of the low gravities in the blue HB stars .
New stellar models indicate that the sloped HBs in NGC 6388 and NGC 6441 might arise from a spread in metallicity , implying that these GCs may be metal-rich analogues of \omega Cen .
The low gravity problem can be largely explained by the radiative levitation of Fe in the atmospheres of the blue HB stars .
We show that the onset of radiative levitation and the drop in HB rotation velocities at T _ { eff } \approx 11 , 000 K coincide with the disappearance of surface convection .
The low rotation velocities of the hotter HB stars may be due to the spin down of the surface layers by a weak stellar wind induced by the radiative levitation of Fe .
We conclude that the impact of mixing and rotation on the HB remains to be clearly established .