A strange error they continually make

When they finally figure out whodunit, we'll get a scene of a constable putting the perp in a police car by pressing down on their head. The reason police do that is when a person is handcuffed behind their backs they don't have much ability to steady themselves and are otherwise likely to bang their heads. But in almost every episode we can plainly see that they are not cuffed. So there's no reason for them to do this head maneuver except that some directors must have watched American programs and thought it looked cool.

The end of the Intelligent Design episode all the way at the end of season 7 is the first time I recall them showing that the perp is cuffed.