Mine does that all the time and I've heard a lot of people mention that theirs do as well, so I imagine it's fine. I actually have a similar question though. Does anyone know if they have to come up to the surface for air or not? For example, if I were to put a screen over the surface, but under the water, so my axolotl could not come to the surface, would it die? (assuming the water is calm and there isn't anything making bubbles). Of course, I'm not considering doing this or anything (that would be horrible!!), but it's just an argument I'm having with my friends over how important their rudimentary lungs are.