As we saw on yesterday’s daf, our Gemara is dealing with the legal status of a non-Jewish slave. Aside from purchasing himself to gain his freedom, a non-Jewish slave goes free if his master knocks out a tooth or an eye (see Shemot 21:26-27) – or, as the Gemara teaches, if the master does other permanent damage to his other limbs.
Our Gemara discusses this rule, and distinguishes between a case where the master physically injured his slave, causing him to become blind or deaf – in which case the slave would go free – and cases where he did not actually hit his eye or his ear, but the trauma of a near-miss causes the slave to lose his sight or his hearing, in which case he would not go free. The Gemara explains that even though we find that damage caused by indirect force is significant (e.g., the owner of a crowing rooster who succeeds in breaking a glass vessel with sound waves would be responsible for the damage), that would not apply to a person, since the damage is not caused by a physical blow, rather because he became frightened – a process that he is responsible for, and his master is not.
The Gemara appears to be describing a hysterical reaction to an event, something that we know can bring about blindness or hearing loss. In such cases, even though there is no physical damage whatsoever, the psychological/emotional trauma does not allow the individual to make use of those senses, and he is effectively blind or deaf. As serious as those situations may be, they still do not meet the requirements of shen ve-ayin (the loss of a tooth or an eye) which would allow the slave to go free.