The hump makes no sense
Makers of this movie didn't seem to understand how much helium you would need to lift an adult man.
Why do people think the hot air balloons are _ENORMOUS_? It's not helium, I know, but helium is not some magic elixir you can just put a drop in somewhere and it lifts up everything. You need LARGE QUANTITIES to generate that much lift, which is why you never see helium used to lift heavy objects in real life.
The tank that keeps helium contained, especially as shown as this movie, would not have been as heavy as the adult man shown in this movie, right? So how can it be so selective?
There's no way you could 'over-inflate' a hump like that anyway. Why put that kind of warning in it instead of just making the hump inflatable only to the perfect size and no further? Why make it out of such elastic material?
The STRAPS required to keep a hump on your back would NOT be strong enough to LIFT AN ADULT MAN without breaking, either. I mean, these are two completely different, separate requirements - to keep something on your back, think about the cheapest backpack - it doesn't require much, especially if it's essentially 'weightless' due to the helium.
To LIFT AN ADULT MAN requires _VERY_ sturdy straps, not only the mechanism would be way different, it would have to be so strong, it would be needlessly strong and too expensive for the 'disguise kit', which, by the way, our inspector can lift with ONE HAND grabbing it from the top!
There would have to be multiple, complicated strap systems and locking mechanisms to make that even possible, so EVEN if that amount of helium was enough to lift an adult man (IT ISN'T!), there's no way the straps would hold.
Nothing about this makes any sense. I realize it's a comedy, but do they HAVE to kill our suspense of belief to the level of a cartoon? There's only so much of crazy stuff someone can stomach.
According to some calculations, you would need around 3571 helium balloons to lift an adult man. That's a LOT of helium! Do you see that much helium used in this movie? No, you don't, not even nearly enough.
If this kind of tiny amount was enough, don't you think people would've been flying all over the place throughout history this way? Don't you think we'd know about it? Don't you think helium balloons would be tiny and effective? Why would ANYONE use these massive, cumbersome hot air balloons, if this kind of small amount was enough to generate that much lift?
Nothing about this helium hump makes ANY sense whatsoever. Also, wouldn't the hump break if it was that elastic and the pressure from lifting an adult man was suddenly added to a product that is _NOT_DESIGNED_FOR_IT_?
No matter how you look at it, this makes exactly as much sense as three fireplaces right on top of each other in the sequel to the modern remake of The Pink Panther movies.
I love Peter Sellers, but sometimes he went too far in stretching the believability. It's also INCREDIBLY stupid and unbelievable that he wouldn't REALIZE he's floating in the air.
The human body is pretty heavy, so if you're suddenly lifted up, it wouldn't be UNNOTICEABLE, especially since those straps would be PAINFULLY TIGHT - imagine someone pulling you up from your backpack straps - that's not an easy thing to ignore, and it would be painful! This kind of pain can't be ignored so easily, and your WHOLE BODY FLOATING OUT THE WINDOW is not something you could be distracted from by a boring phone call!
NOTHING MAKES SENSE!!