Dennis's Birthday

When Peggy reveals she lost her virginity at 14, saying she grew up on a farm, they were poor, and had to make their own fun, Molly quips that they had to put the banjo down eventually. Later, when Mike and Carl are at Dennis' apartment, a banjo can be seen.

Mike and Carl are portrayed as beat cops, not detectives. They would not be allowed to conduct investigations of any kind. Even if they were detectives, they would not be allowed to investigate situations involving friends and/or family members. So what? They are not real cops, it's a sitcom. It's plot, not reality.