Jack and Karen bump chests and hurl insults without missing a beat.
Millions laugh hysterically.
Niles and Frasier engage in a merry game of verbal Ping-Pong. Millions shake their heads at the symmetry and chuckle. It's chemistry, a mysterious element that's difficult to define but easy to recognize. Peter Horton and Geena Davis are perfectly good actors, but the magic just isn't there. Maybe chemistry is as simple as talented actors looking good and working well together.