Bottle confusion

It was December 27th at my inlaws' house, and my brother-in-law was getting my five-year-old nephew ready for bed. He came into the kitchen, took a bottle of milk out of the fridge, heated it up in the microwave and took it to his five-year-old son.

My husband and I looked at each other. There were no words.

Then my brother-in-law came back into the kitchen with the bottle of milk, still full. I breathed a sigh of relief. Clearly my five-year-old nephew did not still take a bottle. With a nipple. No way.

Then we watched my brother-in-law take the top off the bottle, stir in some hot chocolate mix, and put the nipple back on.

When he came back the bottle looked like this:

I don't even know what to say.