Melanie starts with 1 slice of bread that she tears in half, making 2 halves.
She takes both of those halves and tears them each in half, 2 halves x 2 more halves in half = <<2*2=4>>4 pieces per slice of bread.
Melanie is using 2 slices of bread x 4 pieces each = <<2*4=8>>8 pieces overall to add to the blender.
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