Stalagmite vs. Stalactite?

[M.Clifford]

No: HPFGUIDX 106853

--- In HPforGrownups at yahoogroups.com, "Brenda M." 
<Agent_Maxine_is at h...> wrote:
> Hi All,
> 
> -------------------------------------------------------------------
---
> 'I never know,' Harry called to Hagrid over the noise of the 
> cart, 'what's the difference between a stalagmite and stalactite?'
> [PS, 58. UK]
> -------------------------------------------------------------------
---
> 
> Now, am I the only one who feels this line is quite... out of 
line?  Is it important in any ways? 
> Something to do with all the dungeons we see at Hogwarts and the 
> Ministry?
> 

Valky:
Hi Brenda,
No indeed you are not the only one who is interested in this. Now 
you've brought it to my attention, I am too.

Maybe the significance is not in the question but the answer.
Hagrid says "Stalagmites got an 'm' in it"
Now is this just a bit of humour or does it have a deeper meaning.
What are some m words that may be relevant:

Muggle, Magic, Mother, Mudblood... any more?

Now the mites are the cave floor bound formations that travel upward 
toward the ceiling. 

Ok so if it is, at all, a relevant clue to *anything* we will be 
able to parrallel it with something that contains M.....? climbing 
upward.

Stalagtites and stalagmites are just stone formations created by 
gradual deposits of lime etc. 
hmm deposits in a bank double meaning of lime is green...
sorry, I am going nowhere here....

Anyone else?