So there is this post in r/movies I found interesting:
https://www.reddit.com/r/movies/comments/4b623j/battle_of_waterloo_french_cavalry_charge/
I've always found it hard to envision exactly how things looked, and thought this was instructive, but it did bring up a question.
When infantry forms square against cavalry, how do each of the squares keep from shooting members in other squares when the cavalry is in between the squares? Are they supposed to be staggered so that each square has a specific firing lane?
I'd imagine that would be difficult to implement in a hurry during a battle, but you also wouldn't want random firing at close ranges.
Under the British drill at the time, infantry squares were supposed to be arranged point-to-point, so that the greatest mass of muskets along their sides would not be facing each other, and also in a "checkerboard" formation to ensure the greatest distance between them. The risk of blue-on-blue was also reduced by the range limitations of the musket: it was effectively an exercise in futility to try to accurately hit something beyond 100 yards. This was the reason for linear tactics - the only way to guarantee you actually hit something was to "aim" entire battalions and fill the air with lead.
Sources:
Philip Haythornthwaite, British Napoleonic Infantry Tactics, 1792-1815