Can anybody explain to me what does it mean?

code ->
a1 = Array.new(1000000)
a2 = Array.new(1000000)
t = Time.now
1000000.times { |i| a1[i] = i; a2[i] = i }
print "1. Elapsed time: ", Time.now - t, " seconds\n"
t = Time.now
1000000.times { |i| a1[i], a2[i] = i, i }
print "2. Elapsed time: ", Time.now - t, " seconds\n"

results ->
ruby 1.8.6
1. Elapsed time: 0.882 seconds
2. Elapsed time: 11.436 seconds (!!!)
jruby 1.1.1
1. Elapsed time: 1.669 seconds
2. Elapsed time: 2.249 seconds
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