Click <mouse-2> on a completion to select it.
In this buffer, type RET to select the completion near point.

I did a `C-x C-f TAB TAB' in a directory with the file names shown below.
And the output was not very pretty:

Possible completions are:
../ 	./ 	1 	10 	11 	12 	13 	14 	15
16 	17 	18 	19 	2 	20 	21 	22 	23
24 	25 	26 	27 	28 	29 	3 	30 	31
32 	33 	34 	35 	36 	37 	38 	39 	4
40 	41 	41.~1~ 	42 	48 	48.~1~ 	49 	49.~1~ 	50
51 	52 	53 	53.~1~ 	54 	55 	55.~1~ 	55.~2~ 	55.~3~
55.~4~ 	56 	57 	58 	59 	6 	60 	61 	62
63 	64 	64.~1~ 	65 	66 	67 	68 	69 	7
70 	70.~1~ 	71 	72 	8 	9

Hm.  I'm not sure that will show up, because it's just spaces and TABs
used to display this, so I guess the problem has something to do with
TAB handling.

Here's an image instead: