The camera shot behind Malencon when he is lying unconscious on the floor shows his head sideways. When Yar stoops by him, his head is facing the ceiling.
When the new lifeform is being studied, Doctor Crusher takes the viewer through two levels of magnification (factor 5 and 10). But a minute later when she says, "Resume normal scan," the computer only drops back one level.
Different view from the hydraulic room show completely different backgrounds. When Riker and the others run toward the door of the room they run straight along a corridor at whose end the doors is. Shots from inside the room, however, show a wall in the background.
After the life form describes humans as "bags of mostly water", Data remarks that it is an accurate description of humans, as they are over 90% water. In truth, humans are only 50 to 65% water. An android would get this right.
Data makes the claim that only life can self replicate. In actuality, certain man-made devices, prions, viroids, crystals and even fire may self replicate, to name a few. While not all are inorganic, none of these things constitutes life. By the 24th century, there would likely a number of additional examples, as well.
At least twice, Riker taps his comms badge to speak with someone, and it doesn't make its usual beep sound.
Everyone (including the ship's computer) acts like this is the first non-carbon-based life form the Federation has ever encountered. However, in The Devil in the Dark (1967), the obvious inspiration for this story, a silicon-based life form (the Horta) was discovered on a Federation mining colony and identified by Mr. Spock.
As Picard is talking to Mandl through the communications channel, Troi comes to Picard and says that Mandl is alarmed for some reason. No one says to close the comms channel to prevent Mandl from hearing, but he doesn't hear her. The next time Troi starts to speak, Picard closes the channel.
Picard states in his log that the Enterprise is being sent to map the Pleiades Cluster. The Federation and warp drive have existed for well over 200 years, which makes it difficult to believe that the cluster has never been explored until now.
While in engineering, Riker signals Picard up in the observation lounge by calling, "Picard, this is Riker." Referring to a commanding officer by their last name, with no rank, is incredibly disrespectful and out of character for Riker, who usually addresses the captain as 'Sir', 'Captain', or 'Captain Picard' (and, while under the influence of the Q, as 'Jean-Luc').
The character 'Louisa Kim' is called 'Lisa' by Riker when in her guest quarters.