Just received my package!!

I just received my package back!!! There are no tears or openings on the envelope, but it's slightly battered and there was a mysterious hole punched at the bottom corner. I just hope that this won't be the case for my international envelopes.
It's always interesting to see how long it takes to deliver the received package to my dad's office.
On the envelope it says i sent it on the 20th and that it came back to the post office on the 23rd, and i received it on the 27th.
What were they doing with my envelope in those 5 days?? I wish i could find out.