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The storm drain was quite small so the firefighters concluded that the animals that were trapped inside were small, if not babies. When they opened the grate for the animals to come, not one came rushing out. If it had been a mature animal, it would have instantly jumped out knowing that rescue had arrived. But since there was no signs of life upon opening, the firefighters knew something was wrong.
They could hear soft cries from deep into the enclosure and they immediately knew what was on the other end — babies. Probably very scared baby animals that do not know how to save themselves out of a tight situation. Though knowing that they were going to rescuing infants, the firefighters still could not figure out the type of animal that was waiting on the other side. Regardless, the mission was clear. They had to get the babies out as quickly as possible.