What's Wrong With... Planet of Giants

The biggest problem with Planet of Giants was its four episode running time. The third and fourth episodes were edited into one on the recommendation of Donald Wilson as he felt that they were dull, with little incident. The fourth episode - "The Urge to Live" - was directed by Douglas Camfield. The director of the other three episodes was Mervyn Pinfield, and he agreed to let Camfield's name go out on the credits of the recut "Crisis".
This editing caused a few plot problems, as people seem to make huge intuitive leaps based on very little evidence. For instance, telephone exchange operator Hilda Rouse seems to know that the man claiming to be Arnold Farrow is an imposter. Just how often did Farrow call Smithers and Forester for her to know that it isn't him on the line? Surely she would also have heard Forester many times on the phone, so why can't she spot that it is him - even if he is holding a hankie to his mouth?
The Doctor explains early in the story that the full size people will never be able to hear them now that they have been shrunk to an inch in height, yet goes along with a plan to use a telephone to call for help.
Before the cuts, it was the death of the cat which caused Smithers to realise that his insecticide DN6 might be more lethal than intended. On screen, this realisation just comes out of nowhere. Surely he would have conducted enough tests to have known that DN6 killed everything - even the useful insects like bees and earthworms - if they are almost ready to start commercial production.
And just what did the cat eat that had such a high concentration of DN6 that it could have killed it?
Forester's plan to dispose of Farrow's body is to make it look like he died in a boating accident. Wouldn't the bullet hole through his heart rather give the game away?
One of the problems of filming in a very small studio is apparent in episode one, when Susan spots a giant ant's egg, then sees more of them - but they are only a couple of feet away, with the ant itself plainly visible to both her and Ian.
The fly which scares Barbara dies as soon as it lands on the pile of seeds which have been coated with DN6, yet we can see the shadow of its legs continuing to move whilst it is just off camera.
At the end of episode two, Smithers unplugs the sink, and leaves the plug on the side of the sink - yet at the beginning of episode three, the plug is in the sink, as we see the TARDIS crew using the chain to climb up and down. The water flowing down the plug hole also seems to stop very abruptly, without even a drip, let alone a trickle. The sink is also bone dry immediately after use.
The cliffhanger to episode one has the Doctor urging his companions not to look into the cat's eyes - but he's doing precisely the opposite of what he has just told them not to do.
At the conclusion, the Doctor holds up the seed to show they have returned to normal size - but he obviously turns to a camera to do this, turning his back on the companions he is supposed to be showing it to.
Last, but by no means least, just what is the reason for the TARDIS and its crew shrinking? Rather than explain it away as a fault with the ship's dimension control, we get the excuse of "space pressure".