The "That's Odd" feeling is real. And now I understand the term "trypophobia" as a specific example of a more general aversion response which seems common in nature, and might even be hard-wired in the neural-circuits of many animals. The brightly coloured and mottled/spotted patterns found on various insects, amphibians and reptiles may represent more than just simple camouflage. I recall a large black salamander I found which was covered by yellow spots - I recognized it as a local species, not rare, but when I noticed it, despite my interest and curiousity, I felt a clear sense of "weird - ugh - yuck". Now this salamander lives under rocks, under leaves, in rotted-wood, and so on. The existence of the bright yellow spots are not likely related to helping it hide. Why would it evolve such a bright pattern, given its typical habitat? It may be the spot-pattern itself is a weapon, as it seems to provide the creature with a way to trigger a "yuck - leave that ugly thing alone" response in humans, who could be potential threats to the small, slow-moving and otherwise quite defenseless salamader. The pattern of spots on the lotus-seed head seem to be similar to the spot pattern on the salamander. The aversion-response in humans has almost certainly evolved as a protective mechanism to keep us from being poisoned, stung, bitten or burnt when young children. But it is also possible this response is not "hard-wired" at all, but is learned. Once stung by a brightly-coloured wasp or hornet, the child quickly learns to avoid handling this type of creature.
And the harmless salamander's bright yellow random-spaced spots simply mimic
the colour-coding of more effectively hostile agents.
It is possible the aversion to random spotted bumpy/lumpy surfaces may be related to a similar learning phenomenon. We encounter stinking, rotted flesh, and already have the evolutionary systems in place to detect that rotted meat should not be eaten - it smells bad. Really bad. And so, other creatures have an opportunity to evolve displays which - if they mimic the appearance of the rotted flesh - can benefit by the associative trigger of the visual appearance of the rotten flesh, and the chemical response from the smell. If the smell creates a powerful aversion response, the linkage that mammals - not just humans - might make to the visual appearance of the bad-smelling thing, might provide an opportunity for creatures to evolve mechanisms that can take advantage of this situation.
This linkage of stimulus-response, and the ability of the stimulus-response mechanism to be transferred to a different, associated response is well understood - Pavlov's dogs, for example, which learned quickly that the ringing bell meant feeding, and so would salivate when they heard the bell ring, without having to smell the food.
It is also possible the trypophobic response some humans feel, is simply learned, the way many phobias appear to be. The work of B.F. Skinner (creator of the "Skinner Box"), showed that behaviour could be "conditioned", and virtually any stimulus could be made to be associated with any response, given sufficient time, opportunity and intensity of the conditioning effort.
I suspect if a behavioural economist offered to pay $100 for each yellow spotted salamander a person could catch, the typical human would very quickly encode a different internal response to the appearance of the salamander's bumpy, spotted appearance, and it would certainly not be an aversion response.