Horace the Timekeeper - possible mutation?

[fyzygy]

The two plants pictured were grown from an identical batch of seed, under identical growing conditions, etc. The little one got damaged by a snail (?) when it was a small seedling; I cut back the damaged parts, and since then it seems to have adopted a new growth habit, similar to that exhibited by TBM -- prolific new pups rather than fast columnar growth as pictured in the yellow bucket (albeit the strongest of the batch). You can see a couple new pinhead-sized pups forming even in winter. And note the hole that has been bored into one of the pups, possibly insect damage? Anyway, thought I'd put this out there, hopefully to compare notes with other growers who might've come across something similar. I read some theory or another about snail damage and the TBM mutation, maybe this is relevant. 

[tripsis]

Looks like pretty a standard response to apical damage, i.e., the activation of axillary buds via cytokinin production from apical meristem damage. It's exactly what happens when you prune the tip of any plant - it produces branches. In cacti "pups" are simply branches.

[fyzygy]

Good to know. Does apical damage impede growth rate?

[tripsis]

Rate...probably not the actual growth rate, but it would probably slow down the overall rate at which biomass accumulates. Every time apical damage occurs and a plant has to branch, there's a pause in growth. In a plant that size and with that many growth tips, you'll probably find some of them will go dormant and one or two tips will become dominant.