Hello. Is there a way to not to have order of animations in a slide?

For example, a slide has box A and box B. Both have an animation. Now, animation of box A is first and animation of box B is second.

But sometimes during presentation, I may want to have first animation of box B and then animation of box A. I can't know what I will need during presentation, how audience react.

So, is there a way, for example,
*to click on box A when I want its animation to play first and then to to click on box B to play or
*to click on box B when I want its animation to play first and then to to click on box A to play

Sorry for my English.
Thanks.