Magnetic force repel attract, once it starts there's no turning back

"Service was slow at the Old Entomologist," I said by way of exculpation when we returned late to work after lunch. "Head barmaid Evangeline van Holsterin is annoyed with us. Apparently the giant vat-grown brain has been hovering above the Garden Bar again, having used its telekinesis to escape from its nutrient tank. I explained that it gets lost but she just waxed wrother."

"Then she called us both loonies!" Another Kiwi vouchsafed in injured indignation.

Tigris was scrutinising the recent bills, filed in a jar which had in better days contained chocolate Tim-Tams. "We seem to pay a lot of money to the tow-truck company to have the brain hauled back to Riddled Research Laboratory each time. Have you considered infecting it with neurophilic magnetotaxic bacterial symbionts so it can sense the Earth's magnetic field and maybe find its own way home next time?"

Disguising a giant levitating brain: Method #1

"Bacterial symbionts always glow bright green with bioluminescence," I pointed out. "No-one knows why. It must be a tradition, or an old charter or something. Then there would be a glowing green giant vat-grown brain levitating above the garden bar, which attracts attention and is hard to disguise."

"That tow company does seem to charge a lot," said tigris, still scrutinising bills. "Are they really so much better than their competitors? I have half a mind to query the account."

"And be the one who burnt the Topless Towers of Ilium?!" I exclaimed in disbelief.

Anyway, Another Kiwi and I thought this was a good time to shift our attention to our Czech colleagues' observations of magnetoception in numerous mammalian species: ruminants (cows and red deer) but also carnivores (dogs and foxes).

"These are all intermediate hosts for the intra-cellular protist parasite Toxoplasma gondii," I noted.

"Named after Gondor where it was discovered, right?" said AK.

Disguising a giant brain #2

"Since the common element here is T. gondii," I continued, "an ineluctable process of logic leads us to conclude that it must be the source of the magnetoception. So if we inoculate the vat-grown brain..."

"...Then there would be a disinhibited impulsive giant brain levitating above the Garden Bar," tigris pointed out, "which not everyone would view as an improvement." She lost no time in reminding us of the behaviour-modifying effects of toxoplasmosis in rodents, all designed to increase the chance of the host being eaten by a cat (the parasite's definitive host)... the reduced anxiety, the slowed reactions, the attraction to the smell of cat pee.* Magnetic sensing, not so much.

Flegr has accused toxoplasmosis in humans of changing its hosts' behaviour similarly.* Though the attraction to cat pee is only observed among males (which is good news for crazy cat ladies, if they are not fastidious about the impulsivity and slowed reactions of their admirers).**

"Denethor's infection goes a long way to explaining his erratic behaviour," AK vouchsafed.

Toxoplasmosis is known to increase chances of
human hosts impulsively shrinking themselves to
cat-consumable size with a matter transmogrifier

M. paradoxa -- note uncanny
resemblance to Zippy the Pinhead

Then it occurred to us that termites must also have a magnetic sense -- how else could they build their mounds with north-south orientation?! -- acquired, no doubt, from their own symbiotic protists, their cellulose-digesting intestinal flora.

It only remains to tweak the genome of the symbiote Mixotricha paradoxa to adapt it to a new habitat in brain tissue. Then we will have a giant vat-grown brain that not only finds its own way home, but can also subsist on a diet of cellulose! Which will be useful for disposing of inconvenient bills and bank statements.

* The data are rather sketchy and uncorroborated, and accepted mainly because they provide an appealing narrative.

Bonus mind-controlling parasites

** One squees with delight at the existence of a PLoS journal devoted entirely to "Neglected Tropical Diseases". Oh brave new world of author-funded science publication!