B.J. realizes Hawkeye is still alive when he comes across a patient with vertical mattress stitches using white cotton sutures. This is a little baffling as a positive id. Vertical mattress stitching is the most common type of all stitches and white cotton was generally used when nothing else was available: pretty likely at a shelled Battalion Aid station.
Potter and Hawkeye are talking fishing. Hawkeye says he hooked a 30lb Sockeye Salmon but it got away. Fist off there are no Sockeye in the St.Croix river, second Sockeye only get to a size of 60 to 84 centimeters in length and weigh from 2.3 to 7 kg.
In the aid station, when Hawkeye tries to get his hand into the chest of a wounded soldier, you can clearly see his arm is pressed against the soldier's chest and his hand comes back up into the shot for a couple seconds.