Where do we find the practice of a chain-call?
Right after describing the plague of darkness, the Torah describes how Pharaoh calls for Moshe and tells him that he can leave with the entire Jewish people except for their animals (10:24). When did he call Moshe? Some say that this took place after the plague of Darkness, since during the plague of Darkness the Egyptians were not able to move (Bechor Shor).
Others say that Pharaoh summoned Moshe during the plague of Darkness as follows: Although the Egyptians were unable to move, they were able to talk. As such, Pharaoh called his servants who were stationed closest to him and asked them to pass on a message to call for Moshe. The servants spread that message to other Egyptians that were within their hearing range, and eventually this chain-call reached Moshe, and he appeared before Pharaoh (R' Chaim Potiel).
Pharaoh only called Moshe and not Aharon (10:24) as he was too embarrassed to humble himself and allow all the Jews to leave in front of both Moshe and Aharon.
When were Revenge and Curiosity two massive tests for the Jewish people?
The Chasam Sofer says that during the plague of Darkness and Makkas Bechoros the Jewish people faced two immense nisyonos (challenges) to see if they would comply with Moshe's instructions or not. Overcoming these two tests was the merit they needed in order to were told to go look and see where the Egyptians hen the word spread that HaShem had warned kept their money, so that they could ask them that He would strike the firstborn from the for it when they left Mitzrayim. It was, however, firstborn of Pharaoh who sits on his throne to tempting to take their possessions, kill their the firstborn of the maidservant, some reasoned oppressors who were kept in Darkness, and that the captives in the dungeon are on a immediately leave Mitzrayim. The fact that they lower level than that of the maidservant. They listened to instructions and did not take revenge therefore mistakenly concluded that prisoners are and escape was a tremendous source of merit for excluded from Makkas bechoros, and they placed them. Likewise, by Makkas Bechoros, the Jewish people were instructed not to leave their houses for the duration of the night. Imagine what it was like in a Jewish house when loud shrieks could be heard throughout the night. They felt extremely curious to see what was happening. Perhaps it was their fellow Jews who were suffering? Perhaps there was some kind of attack or war happening? Perhaps there was a massive fire or a flood? The restraint that they practiced by not going to find out what happened all around them, served as the second main merit with which they were able to leave Egypt.
