As Mata Hari is before the execution squad, the officer commands "Present... arms!" and the squad begins pointing their rifles forward. French Army command "Présentez...armes!" signifies only to take the rifle from the shoulder strap and bring it in front of you pointing upward, as the case is, with the long WW1 rifles.
After Von Krohn has been murdered, he is breathing visibly.
There is a blind man in Paris outside Mata Hari's lodging, or rather a spy pretending to be blind. He has a white cane and a seeing eye dog. The white cane was adopted to mark a blind person first in England in 1921. Also training of seeing eye dogs began first in Germany in 1915, so these both would have seemed odd in WW1 France.
Mata Hari (Sylvia Kristel) is shown dancing bare-breasted several times in the movie. In real life, Mata Hari never danced bare-breasted as she was self-conscious about having small breasts.