Towards the end of the film, before the final shooting in the distillery, Fernand says he has a wedding at 10 (supposedly 10:00AM). Later on, at the very final shot, after the car explodes in front of the church, the church clock clearly indicates 06:30PM. In France, wedding ceremonies never last for 8 and a half hours...
No doctor would leave air in the syringe before injecting.
When punched by Lino Ventura, the wall against which Freddy falls buckles. Georges Lautner points this out in the director's commentary.
The close up shot on the doctor's syringe shows that he is purging or flushing the air out whilst keeping the syringe horizontal. Not accurate.