There's a risk here of getting a `StaleElementException` if the problem gets reloaded in between when you find the element and when you click it (same for the `mouse_over` call above).  The ui helper `world.css_click` protects against this by retrying on such exceptions.  There isn't an equivalent for mouse over, but it would be easy to add one in `common/djangoapps/terrain/ui_helpers.py`