I assume you mean mousse, and not some ickle rodent that you've tried to mince up! lol
I would add my mix a mousse powder to the pack (usually half as much again as they say on the tub) then get my liquidiser running with really cold water in it about 350ml, and take off the lid (carefully) and pour in the pack. Whizz it on fast speed for a good 20 secs then pour into a dish and I would put mine in the freezer for about 5 mins (sometimes longer if I forgot) Turned out perfect every time x x