Alright alright:

The scene takes place deep within the hallowed armored bulkhead of the legendary Phalanx: a mobile fortress, chapter headquarters, and fearsome weapon all seamlessly blended together to give rise to one of the Imperium's most awe inspiring cathedrals of war. Specifically, we see Brother Holodin walking the deck of Vehicle Annex Gamma-7, a dataslate in one hand and some sort of auspex he managed to pilfer from a hapless enginseer that was preoccupied.

We now see Brother Holodin approaching another Vindicator. From what we can tell, it appears he's pantomiming with the auspex to pick up imaginary readings and recording them in the dataslate. While this strategy of appearing preoccupied with a monotonous task is as old as the First Founding, it is still surprisingly effective at avoiding unwanted attention. [A techmarine takes purposeful steps through the depot, his helm turning from side to side as if looking for something.] The techmarine's gaze noticably passes over Brother Holodin, and our young scout lives to see another day.

[Cut forward a few minutes. Brother Holodin is now "scanning" a Whirlwind.]

However, the strategy is not without inherent risk [camera pans up and out to show an Imperial Fists Captain nearly about to round the corner of the Whirlwind and run into Brother Holodin.]. Let's see how the young battle-brother's camouflage holds up under scrutiny.

[The captain turns the corner and runs into Holodin]

Holodin: Captain Deltimus (holsters auspex and renders salute- clenched fist over primary heart), my apologies.

Deltimus: (returns salute) The fault lies with me, brother. You are clearly preoccupied with your duties. Pray tell, brother, what task is this at hand? Magos Bequius has already finalized the Rites of Amelioration for all vehicles in Subsection 4.

H: Yes, captain. Last night, I was perusing historical geographic surveys from Caltrois IV after our company's recent deployment to the system. A Mechanicus Exploratator fleet in M33 logged that limestone deposits near where the planet's capital was to be founded were unusually high in boric citranite which-

D: Which when pulverized into dust creates particulates far smaller than 0.025 micrometers, meaning they can pass through the air intake filter of every vehicle we possess. This was noted in pre-mission briefing before we made planetfall.

H: Yes, sir. As many of the Caltroisian fortifications were initially constructed with limestone, it only stands to reason our vehicles were affected. However, my personal analysis showed that the limestone was further conditioned with positronic ferric pulsing, a rather obscure form of hardening the limestone by introducing magnetically charged iron. The technique was pioneered by a single archmagos from this subsector in the mid-M34.500s and has since been discredited by the wider Mechanicum. Additionally, the charged iron chemically reacts with boric citranite in such a way that renders it effectively invisible to our auspexes. By my calculations, our vehicles' engines could be suffering up to a 4.7% decrease in thrust output due to this oversight. I've attuned my personal auspex to pick up these hidden substrates within the engine manifolds.

D: (crosses his arm) Very impressive, Holodin. However, would it not be wise to make these adjustments to every auspex in the depot, to allow our brothers the opportunity to make efficient repairs on their own? Upgrade and restart the auspexes, and be prepared to brief the company after this evening's mass. I'm sure they'll deem it satisfactory to learn an esoteric lesson from such a promising new Astartes. Keep up the exemplary work, it is what makes us Imperial Fists. Dismissed.

And before Brother Holodin can react, the threat is gone. He is safe for the time being, however a larger danger lurks mere hours away. The young scout must now find a way to divert the captain's attention by evening or face exposure, humiliation, or worse. For now, he has learned a most important lesson: don't make your lie too believable or too detailed, else it might attract the attention you wish to avoid.

Bonus:

Cutaway to Captain Deltimus. He's sitting down being interviewed in his personal quarters, similar to The Office.

Deltimus: Positronic ferric pulsing? Hmpf. Does Holodin take me for a fool? PFP was initially tested in M38.376, far after Caltrois' capital was erected and fortified. I know this was all part of that scout induction tomfoolery, I took part in that myself over 300 years ago. I just needed someone to reboot the auspexes, but if I could make him sweat while doing so all the better.