IMDb Trivia page:
What does the title mean?
The phrase dog days refers to the hot, sultry days of summer (July
and August in the Northern hemisphere and January and Februrary in the
Southern hemisphere). The name comes from the ancient Roman dies
caniculares, which was associated with the 'dog star' Sirius (so named
because it is the ...
On the one hand, Sonny did state that if the police didn't cooperate, bodies would start flying out the door.
However, later on in the movie, while Sonny did look non-violent, he made himself out to be the only one who could control Sal, who he portrayed as a cold-blooded killer - e.g. if anything happened to him while he was out talking to the police, Sal ...