Acts 14:14

But when the apostles Barnabas and Paul heard of it, they rent their garments, and sprang forth among the multitude, crying out.

When they heard of it ... has the meaning of "when they became aware of what was taking place." The rending of the garments was a traditional reaction to blasphemy; and the offering of sacrifice to mortal men was thus interpreted by Paul and Barnabas. Being unable to get attention otherwise, they frustrated the plan by running among the people and crying out as in the next verse.