Frank Castle discovers a disk with the word 'micro' written on it. In the earlier Punisher comics, he was assisted by a computer expert / weapons designer named Microchip.
This is the first episode where Punisher wears his famous skull logo on his bulletproof vest.
When Matt tries to "listen to the city" in order to locate Karen, he gets overwhelmed with the numerous sounds he has to interpret and needs coaching from Elektra to focus. In Daredevil mythology, Matt's powers force him to have to interpret everything around him at a remarkably fast rate. He hears, smells, feels and senses everything within range of his Radar sense and has to decipher each one because there's no way for him to ignore, nor tune them out; he lives in this world in constant flux so it takes great mental discipline to control his abilities.
At 18:05, the only instance in the series where Daredevil uses his billy club to swing. The character sometimes uses his club to swing or zip-line to another building or unreachable area in the comics and other media.