Blooper

Lansing watches the stick sinking in a pool of liquid, but in a later long shot the stick in seen firmly standing in dry ground.

Near the end, when John is backing up the jeep to the pit, he is sweating profusely. In the next scene his face is dry.

Out of interest, the Thompson sub machine gun was issued to British forces. It was issued to regular army, Home guard (later TA) and especially auxiliary units. It was also issued to commandos, both army and later RN. Originating from the early twenties, the Tommy gun was issued to Brits much later, and some stayed in service for a very long time.

At 26 minutes, when Royston shows his colleague Peter an exploded jar of tritium, he asks him how long it will remain radioactive. Peter guesses 30 years. Royston says that's close: it's 28 years. Tritium has a half-life of 12.3 years which means that in 28 years it will still retain 20.6% of its radioactivity. After 100 years, only 0.4% will be left, but it would still be detectable.

After the blob starts wandering, the background music is so loud that the dialogue is frequently almost inaudible.

There's no explanation given for why the creature returns to the fissure after every meal.