The first map operates on a list of 3 strings in which each string only contains a series of "x"s. Thus the tr command in the map is used to return the number of "x"s in each string it is fed. Ths resultant list is (9,11,11).
The next map adds $cells (which is 100) to each of these numbers and prints the ascii value of these numbers, which prints out moo
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