Help animated images in epub

Hi everybody,

I'll try an explain what kind of help do I need. I use calibre to convert docx files into epubs, so I do it very simple, sometimes my documents had an image (static one), and I never have any problem with that, recently I convert a document that I didn't realize had an image that it was a gif file, the way that I notice it was because in the epub version it was animated, this obviously make me realize that I can put animated images in my documents and have them in the epub format.

My problem is that I didn't did anything different with the one that has the animated image, but when I try to do it on purpose, I couldn't do it, I insert the gif image in the document, change the size, etc, but it simple doesn't even put the image without any animation, it just like it doesn't even exist one.

Can anybody help me understand this, I will really appreciate it, is driving me crazy not to know why.

Thanks in advance
:)