Witness

1. In version 13, you can GET IN just about any object, with numerous buggy results. You can GET IN CARVED CHAIR without Mr. Linder complaining, and thus be sharing the chair with him when he's shot. If you GET IN something you're carrying, then any reference to yourself asks which one you mean. If you GET IN ME, you can DROP ME. If you GET IN something after meeting Linder but before he takes you to the office, he follows you into it. When it's time to go to the office, he takes you out of whatever you're in. The possibilities are legion.
2. In version 13, if you drop the handcuffs then you can't pick them back up. You're told, "You shouldn't release a suspect until your work is finished here."
3. In versions 13 and 18, you can get the chunk of putty or the piece of green wire before the window is broken, using EAT, READ, or LIGHT.
4. In versions 13 through 20, EXAMINE WINDOW gives the same description (including the white wires and electric relay), whether you're inside or outside the house, but EXAMINE WHITE WIRE says, "There's no wire here.", when you're outside.
5. In versions 18 and up, you can GET CUFFS when you're already holding them. Each time you get the response, "You are now carrying the pair of handcuffs."
6. All versions have a serious bug in the use of IT. You can interact with objects you haven't even seen yet, using IT. For example, you can EXAMINE LIQUOR CABINET THEN OPEN IT, or FIND MYSTERY THEN READ IT from anywhere in the game. Another interesting thing to do is EXAMINE WOODEN CHAIR THEN SIT IN IT on the first turn. This doesn't get you inside the house, but Mr. Linder tells you his story and hands you the threatening note.
7. In all versions, although you can't GET objects inside a closed container, you can do just about anything else to them, as if they were visible in the room. If they're otherwise takeable, then you can even pick them up using EAT, READ, or LIGHT.
8. In all versions, the dresser in Linder's bedroom can be closed, but not opened.
9. In all versions, if you PUT something ON BED in Monica's or Phong's room, it's gone forever, unless you remove it using IT right after. If you LOOK ON BED, you see everything you've put on either of these beds. PUT something IN TUB has the same problem. If you PUT something IN CLOCK, it's just gone; you can't even see it using LOOK IN CLOCK.
10. In all versions, HANDCUFF MONICA TO something puts the cuffs in it. So if you HANDCUFF MONICA TO CABINET THEN OPEN CABINET, you "see a pair of handcuffs" inside it. HANDCUFF MONICA TO CLOCK or BED makes the cuffs disappear. After you do this, UNTIE MONICA picks them back up, but they don't show in your inventory. If they're the only thing you're holding, INVENTORY gives no output. If you DROP them they don't show in the room description, and you can't pick them up again.
11. In all versions, a number of unexpected objects can be locked and unlocked. These include the mystery book, refrigerator, bathtub, dresser, and cupboard.
12. In all versions, if you try to LOCK or UNLOCK anything in the presence of the living Linder, he says, "Don't leave yet. We're just getting started."
13. In all versions, if you KNOCK ON a DOOR with someone on the other side, you get, "Someone shouts, "Go to the front door!"", unless it's the front door. In that case you get, "A muffled voice says, "Come in!"". This even works if you KNOCK ON FRONT DOOR from Entry when someone's on the porch, or if you KNOCK ON TOILET DOOR when Monica's in the toilet room.
14. In all versions, you can TELL anything visible ABOUT something, producing such responses as, "grandfather clock lets out a loud yawn.", or "broom appears to be getting impatient." You can also ASK anything visible ABOUT something nonexistent such as GREEN KEY or something not in the game yet such as TICKET, producing such responses as, "bed looks confused. "I don't know anything about any ticket!"".
15. In all versions, you can ASK any character FOR DRINK or CIGARETTE at any time, whether present or not. You can even ASK MR. LINDER FOR CIGARETTE when he's dead, and he smokes with you.
16. In all versions, you can EXAMINE CIGARETTE anywhere. You get, "All you can see is an ashtray full of butts."