Why the irish flute has 2 holes more, in the bottom???
http://www.mikelceltic.com/wp-content/uploads/2014/05/Irish-Flute.jpg
Venting. The length of the flute for the note D actually is to that 1st open hole. The Vent holes are often approximately where the low C & C# keys (normally open keys) would be on a keyed flute.
According to flutemaker Phil Bleazy’s web site, "Players of Irish music have long favoured two types of flute from the 19th. century, namely the Rudall Rose & Pratten. Many of these “Irish flutes"had the keys removed and the associated tone holes blocked up to facilitate sliding between notes and other techniques … which are the soul of Irish flute music. A characteristic of the Irish flute is the foot joint with it’s [sic] two open holes left by the removal of the C & C# keys. After many years of making these flutes I have yet to find one which is improved by this redundant joint. Consequently my “Irish flutes” carry my own design of foot joint, which, sadly, means that the Morris dancers have no where to tie their ribbons. I’m sure no one else will mourn the loss.”
It must be true, it’s on the internet.
Best wishes.
Steve
There are no stupid questions, just stupid answers…uh, wait a minute…
Now i feel less stupid!
Many thanks, mates
Good advice from Brian Finnegan: Do not use raisins to block the holes. I’ll spare you the details. 
The “King of the Wooden Flute”, Seamus Tansey, advocated sultanas. . . . 
Bob
And yet, there are keyless flutes in D made without the venting holes - Burns Folk Flute & Copley 3-piece come to mind, perhaps there are others too.
My McGee GLP has only six holes. I’m waiting on a Martin Doyle flute. His flutes also do not have the extended foot with additional holes. From his website:
I do not add long foot joints to my flutes unless C and C# keys are needed. The reason for this is a flute that has as it’s bottom note a D note provides a stronger D than a flute with a C foot joint. The long foot joint tends to make the D note more equal in quality to the other notes on the flute, whereas in Irish music it is desirable to have stronger D notes as the keys that the tunes are played in are predominantly D and G.
So i assume that i can shorten the footjoint without ruining the intonation?
If you’re talking about cutting off the “excess” - NO!!! Flutes with the extra toneholes are tuned to work with the extra length of sounding material, which may entail internal dimensions being slightly adjusted. You would probably be close, but your intonation would definitely suffer. If you don’t want the extra holes, just buy a flute without them - as mentioned above, many makers offer the short foot option.
Pat
What he said 
I have two flutes from the late 1800’s, one with a short foot(Eb/D#) key, and one with the longer foot, C# and C keys. With the cork properly adjusted they have nearly perfect alignment of their harmonics. They exhibit slightly different approaches to the tuning in their lower bore diameters. The alignment of their harmonics is crucial to the tonal possibilities available to the performer. Their ‘honk’ on the low end. If you cut down a long foot you will destroy this harmonic balance.
Bob
Many thanks, mates. I’ll put my razor saw away 