  The de Broglie - Bohm Interpretation of Quantum Mechanics assigns positions
and trajectories to particles. We analyze the validity of a formula for the
velocities of Bohmian particles which makes the analysis of these trajectories
particularly simple. We apply it to four different types of particle detectors
and show that three types of the detectors lead to "surrealistic trajectories",
i.e., leave a trace where the Bohmian particle was not present.
