17 "Home Alone" Details That Are Both Funny And Interesting
The breaking grocery bags gag was achieved with strings.
1. Kevin's plane ticket and passport get accidentally thrown out after the spilled milk incident, which explains why no one initially notices Kevin isn't on the flight.

This is kind of a famous blink-and-you'll-miss-it detail, but I wanted to mention it in case you didn't know!
2. There's a dummy of Uncle Frank sitting all alone and doing nothing in the background here.

It is possible that it's not a dummy, but the figure NEVER MOVES AN INCH during this scene. Also, Uncle Frank is supposedly watching a movie with the older kids at this time (remember, Kevin isn't allowed to watch?!) — and he's clearly not doing that here. Not to mention, Uncle Frank comes down from upstairs just a few moments later when the pizza arrives.
3. The red Christmas bow that goes flying off during the storm ~magically~ reappears back on the lamp post a few seconds later.

However, it is missing for the rest of the movie after that. So I'll give this tiny continuity error a pass. ¯\_(ツ)_/¯
4. Just like Kevin's dad said, the garage door is in fact left open, but WEIRDLY the cars aren’t even pulled all the way into the garage.

This was most likely done on purpose by production for lighting reasons, but it's still funny to notice.
5. Kevin can't find his toothbrush because his mom packed it away for their trip.

So the whole accidental and dramatic theft of the toothbrush ("I'm a criminal...") happened all because Kevin doesn't know how to pack a suitcase.
6. The "robe" Kevin uses to disguise himself with in the nativity display is actually just a curtain from the display...

Nice setup, Chris Columbus.
7. …and someone at the church apparently fixes it, because it's hanging back up again when Kevin returns later on.

8. Kevin cut out the basketball from the Michael Jordan poster in Buzz's room and had to stitch Jordan's arm together with tape...

9. ...although ~magically~ the poster appears altogether again, basketball and all, in Buzz's room later in the movie.

It looks like MAYBE Kevin taped it back together.
10. Several of the mannequins Kevin uses for his makeshift ~party~ can be seen in the basement earlier in the movie.

11. You can see what looks like tiny rocks (or maybe grains of salt?!) being tossed at the spider to make it move in the bathroom.
That poor spider's prob like, "WTF?!"
12. When Kevin's grocery bags break, the large container of Tide detergent is missing.

It's either a continuity error or the detergent was too big to fit in the bags for the gag. Either way, I didn't notice this until several viewings later!
13. And, in case you've always wondered, the bags breaking gag was achieved with string, which you can see if you look closely enough.

MOVIE MAGIC.
14. It's not easy to hear, but if you listen, the basement furnace actually says, "Hello Kevin."

In fairness, this is in Kevin's imagination, but it's still funny and random.
15. Kevin's mac and cheese dinner appears to be a totally different frozen dinner moments later when Harry enters the dining room.

The prop department, probably: "No one will notice."
16. If you're wondering why there's a doggy door in the house, but no dog ever appears in the movie, it's because the McAllisters put the dog in a kennel for the trip.

Although I'd like to know what kind of dog they had?
17. And finally...apparently, Harry is married.

Well, well, well...