20. Kill the duck
The rubber duck is also a physics object. But if you shoot it into the water, it sinks without trace. Presumably because it's full of bullet holes?
21. Get the sleeping pills
Don't forget to pick up the sleeping pills from the bathroom. There are a couple of uses for these...
22. Spike the head guard's coffee
Like putting sleeping pills in the head guard's coffee while he isn't looking. He'll eventually feel funny and leave the room, whereupon you can steal his security card to get further into the building.
23. Drug the chef
Or you can put sleeping pills into the food that the chef is preparing in the kitchen, sending him to sleep in a chair so you can nick his clothes.
24. Dress as a chef
There's no denying the fun in stealing the chef's outfit, mainly because Agent 47 goes through an incredible transformation, from looking like a big scary assassin to looking like a big scary assassin dressed as a chef.
25. Or put your outfit away for later
If you don't want to dress as the chef just yet, you can always store him in a cupboard along with a security guard. He'll have trouble explaining that one when he wakes up.
26. Turn invisible
That same cupboard is an excellent hiding place. See how open the door is? See how that guy's looking right at you while searching for the very person that you are? Well, he hasn't spotted you. That's the power of a small cupboard.
27. Steady your bead (curtain)
The bead curtain's physics are great fun, falling around Agent 47's frame as you walk through, then back again, then through again until you get bored.
28. Play it again, Sam
There's an 'accidental' kill waiting to be ticked off in your notebook involving this piano. Pressing Y to remove the support brings the lid crashing down, as does shooting it. How could that be used to your advantage...?
29. Indulge in some 'instinctive voyeurism'
Your instinct mode acts like Batman's Detective Vision, allowing you to see outlines through walls. Your first target is female and taking a shower, which you can see if you trigger your instinct before you open the door and start the cut-scene. Technically, it's just Agent 47's imagination, but still...