For the choux puffs: Preheat the oven to 375 degrees F.
Put 1/2 cup water, the milk, butter, sugar and salt in a medium saucepan and bring to a boil. Stir in the flour all at once and continue to stir and cook for a minute or two, until there is a light coating of flour on the bottom of the pan. Remove from the heat and put the dough in a mixing bowl. Beat in 6 of the eggs, one egg at a time, until the dough is smooth and elastic.
Spoon the dough into a large pastry bag fitted with a plain #2A tip and pipe 1-inch balls onto a baking sheet lined with parchment paper. Whisk the remaining 1 egg in a small bowl with 1 tablespoon water. Brush the dough balls with the egg wash. Bake until golden brown, 20 to 25 minutes. Let cool completely.
For the ganache: Heat the cream in a saucepan or in a microwave until scalding hot.
Put the chocolate chips in a medium heatproof bowl, pour the cream over the chips and whisk until smooth.
Beat the heavy cream in a heavy-duty mixer with a whisk attachment until stiff peaks form. Put 1/2 cup of the whipped cream in a small pastry bag fitted with a round #7 tip. Use this for piping the eyes.
To make the mousse, fold 2 cups of the ganache into the remaining whipped cream until well incorporated. Put this mixture in a large pastry bag fitted with a round #2A tip for making the head.
Put 1/2 cup of the remaining ganache into a small pastry bag fitted with a round #3 tip for making the irises.
To assemble the chocolate moose: Cut the top off of each choux puff to make a small, irregular circle. Cut this in half to make the two antlers for each moose. Pipe a roughly T-shaped mound of mousse in each puff to make a head. Place the two halves of the puff top sticking into the outer edges of the T and flaring outward to make the antlers. Use the whipped cream to pipe little eyeballs next to each other at the top of the T. Use the ganache to pipe tiny dots on each white eyeball to make the irises. Feel free to add other details with the ganache, such as eyebrows, nostrils, sunglasses or smiles. These are undoubtedly happy moose. Taste one if you are doubtful. Happy moose choux taste great!