what does .strip()[-3]mean in python code example

Example 1: python strip

txt = "  test    "

txt.strip()
#Output: "test"

txt.lstrip()
#Output: "test    "

txt.rstrip()
#Output: "  test"

Example 2: python strip()

a = "  smurf   "

a = a.strip()
#remove space at begining and end of string
print(a)
#smurf