Yea it was early in Heisenberg’s criminal career, so he he was still soft and naive.

Small spoilers

They were keeping a gangster in the basement, tied to a pole, since quite a long time. Heisenberg didn’t know what to do. The gangster became friendly and closer, at least it seemed. Then Heisenberg broke a plate next to the gangster. He said he’ll come back with a new plate. He collected the pieces and went up. There he realized the gangster had taken a shard for himself. So he decided to kill him. Heisenberg strangled the gangster from behind, and as he did so, the gangster tried to reach Heisenberg with the shard, but was too far and managed to cut his leg.