Create a trigger for mouse animation

I haven't seen a way to trigger the start of a mouse animation other than the start/stop on the timeline. However, if this is the only slide where you plan to use the mouse, you could easily add a mouse graphic, trigger a fly-in animation, add a "click" audio, and grow in a red circle highlight to go with the click sound. The built-in features of the Storyline mouse show their effectiveness and flexibility on multiple slides with continuing mouse activity. For just one emphasis, I think I'd just build the animation.

Alternatively, you could add an object off-screen in the additional layer and have it change states at the end of the layer's timeline. Then set a variable to change when the when the object state changes. Lastly, set a trigger to start the the animation when the variable changes.

Thank you both for your suggestions.

In the end I did it using just the timeline. If users click to view the other layer the base layer pauses until the additional layer is closed. The mouse and a circle appear later along the base layer timeline. Once those two have finished loading, the image in the final square appears (again, by placement on the timeline rather than triggers).

I will experiment with off-screen objects and variables as suggested by Kristian for future reference as this would make it more controlled.

Many thanks

Hazel