Hi Tal,
What I believe is happening is that the gif is starting from the middle, so that it seems like it walks twice.
I'd try to add the following action just before showing the gif stimulus:
function reset(){ var el = document.querySelector('.minno-stimulus[data-handle="stim-handle"] img'); el.src = el.src; }
What this does is reset the gif just before it displays - it should be reloading from cache so you don't lose much in terms of timing.
Note that you should replace "stim-handle" with the handle of the stimulus you're trying to replace.
best,
Elad