Storm only really does it after an hour-long play with a feather toy. Benji was getting all worked up yesterday though, we ordered some cheap toy from zooplus, a little bird attached to flexible string that you hook on to the door frame, and obviously when they run off with it, it pings back...well you can probably picture what he was up to :D He went mental with it for an hour and a half, had to take it away from him in the end as he was panting like crazy! Once he calmed down he just passed out in to a deep sleep so seemed fine. Think it was just the scorching heat yesterday!