FlickerAnimation.xaml

<Storyboard x:Key="FlickerAnimation">
  <DoubleAnimation Storyboard.TargetProperty="Opacity" AutoReverse="True" RepeatBehavior="Forever" Duration="0:0:0.5" From="0.0" To="1.0"/>
</Storyboard>

<!-- ... -->

<Style.Triggers>
  <DataTrigger Binding="{Binding SomeProperty}" Value="SomeValue">
    <DataTrigger.EnterActions>
      <BeginStoryboard Name="Flicker" Storyboard="{StaticResource FlickerAnimation}" />
    </DataTrigger.EnterActions>
    <DataTrigger.ExitActions>
      <StopStoryboard BeginStoryboardName="Flicker" />
    </DataTrigger.ExitActions>
  </DataTrigger>
</Style.Triggers>