  We provide some considerations on the excitation of black hole quasinormal
modes (QNMs) in different physical scenarios. Considering a simple model in
which a stream of particles accretes onto a black hole, we show that resonant
QNM excitation by hyperaccretion requires a significant amount of fine-tuning,
and is quite unlikely to occur in nature. Then we summarize and discuss present
estimates of black hole QNM excitation from gravitational collapse, distorted
black holes and head-on black hole collisions. We emphasize the areas that, in
our opinion, are in urgent need of further investigation from the point of view
of gravitational wave source modeling.
