Photosensitive epilepsy (seizures triggered by sudden changes in luminescence) doesn't affect too many people, but it's an awful condition and sooner or later one of your users will have it. The general rule here is "no more than 3 flashes per second." [1]
You probably don't have a good design reason to use strobe lights anyway. Slow those .gifs down, please.
[1] http://www.w3.org/TR/UNDERSTANDING-WCAG20/seizure.html