What have you done to my lights?

Our bathroom light bar holds six bulbs. We had let them burn out one at a time until only two were left burning. Cari went out last week and purchased new bulbs. When I was in the bathroom that evening, I noticed all the lights were working. There was a bit of dust still on two of them, so I knew that she didn't change those. A quick quarter turn to the left and they went out.

A bit later, Cari came out of the bathroom complaining that the only two bulbs she didn't replace stopped burning. I couldn't hold back my laughter as I walked past her and tightened those bulbs.
She didn't love the joke as much as I did. The next day at work, I told this story to my friend, Rick. As I told my story, Rick got this crazy look in his eye and face lit up. This is an expression that I am very familiar with. Rick provided me with an idea to continue my joke on Cari and he provided the props needed.

Last night was MY moment. The plan was to wait until Cari went to sleep Saturday night and then make my move. She would realize my genius Sunday morning as she was getting ready for church. The problem was that I fell asleep on the couch waiting for her to fall asleep.

I woke up at two am. After checking that she was asleep, I went and got the small disks. I went in the bathroom with a flashlight and closed the door. As I unscrewed each bulb I held my breath. It seemed like I was making so much noise. With the bulbs out, I popped in the small disks that cause a bulb to randomly flash on and off. While putting the bulbs back into the sockets, I thought I heard Cari moving about. At that moment I was about half done with my setup. For a minute, I thought about abandoning the project. If she woke up and went into the bathroom before morning, my joke would be ruined.

After another minute of holding my breath, I finished with the bulbs. I flicked the switch and all the bulbs came on. Then, randomly, they started flashing on and off. SUCCESS! I turned the switch off and quietly snuck into bed by two thirty this morning.

At seven, Cari woke me up, "What have you done to my lights?"
I thought about playing dumb, but the big smile on my face was going to give me away. I turned my head away from her and asked what she was talking about.
"All the lights are flashing. You need to fix this. How did you do that?", she continued.

As I got up to start un-installing the flashers, I was laughing. Cari's last words this morning as we were getting in the car for church, "I will get you back."