55 Years Later, Alcatraz Escapee sends this note.

Feeling Chippy

Every night between roughly 5:30 p.m. and 9 p.m., they had to physically chew away at the rock in their individual cell to gain access to the ventilation system. This was done so they might flee. They would take off the grate from their cell and nibble away at it using the spoons they had pilfers or bits of wood they had acquired from places where they worked during the day while nobody else was looking.

When the grand plan was fully carried out, this would prove to be the most time-consuming element since it would take months and weeks to subtly chew away and eliminate the boulders they had gathered for several hours every day.