Continuity mistake: When poor George is about to be sucked down the drain by the blob, he is looking at his hand. When the blob attacks him, he's holding on to the sink with both hands.
Continuity mistake: When Paul calls Sheriff Herb, the window is closed. Who opened it for the blob to escape?
Continuity mistake: After Meg and Kevin climb the sewer pipe that leads to the street, Meg is unable to fit in the grate. In one shot she's trying to fit her head through the grate but in the next shot she is not. (01:12:22)
Answer: In both the the 50's original and 70s sequel, the majority of the Blob effects were created using a thick silicone gel colored with red vegetable dye; its movement was essentially controlled by gravity, just letting the goop run downhill and angling the camera to provide the illusion that it was moving horizontally, vertically, or straight at the audience. The original film also employed a large barrage balloon (or weather balloon) covered in the colored silicone goop for shots where people are actually consumed by the Blob. The 1972 sequel additionally used a preposterous rotating spit covered in red plastic, mounted in front of the camera, to provide the Blob's point-of-view as it steamrolled toward its victims. The 1988 remake used much more sophisticated practical effects such as robotics, latex prosthetics, pneumatic tentacles, et cetera, which were directly inspired by John Carpenter's 1982 special-effects-heavy horror flick, "The Thing." For the last couple of decades, there has also been talk of a major CGI reboot of "The Blob," but it has yet to materialize.
Charles Austin Miller