def _plot_vels(vels, labels, title=None):
    """Plot trial velocities as a stem plot"""
    trace = dict(y=vels, x=labels, mode='markers')
    layout = dict(title=title, xaxis=dict(title='Trial', automargin=True),
        yaxis=dict(title='Speed (m/s)'))
    return dict(data=[trace], layout=layout)
