Wait For It...
by Kegler

One letter in each column moves in a certain way, creating a new Down word in each case. Left to right, these letters provide a relevant phrase.

Wait For It... grid

Across
1Notice bit of primordial ooze (4)
4Aims for tourist attractions, we hear (6)
10Small birds inside mines, an endless number? (6)
12Crazy person circles Silver Lake (6)
13Atlas rocket stage schedule is missing date (5)
14Actor Conway recalls eastern university (3)
15Dog starting to like certain exercise (4)
16Talk one time after church (4)
17Picture our group returning Buddhist scripture (5)
18Most revered emcee internalizes falsehood (7)
19Poets, heartless asses, broken up by unfinished paean (7)
21Ocean phenomenon involves large wave? (5)
22Whimper as table collapsed (5)
24Customers with money acquiring jetliner, essentially (7)
29Electra's cooked sweet stuff (7)
32Sings jazz with Southern jazz fans (5)
34Traveling solo in Norwegian city (4)
35English anger a member of the United Kingdom (4)
36Publicity beginning to overwhelm paid athlete (3)
37Story of First Lady getting in long line (5)
38Six-line poem, “Tsetse Flies” (6)
39Live with obscene desire (6)
40Certain artist's number receiving copyright (6)
41Storm – not Monday, but before long (4)
Down
1It holds a spot for sports highlights retrospective (6)
2Peak of importance, after husband replaces wife (6)
3Spot trace of oak in British beer (5)
4Alarm rattles horribly (7)
5For example, upturned cover is very cold (5)
6Mornings after starting to haunt amateurish actors (4)
7Cry, with uncle in picture (5)
8Rocky hill, clear and parched (6)
9Some Cajun leaders process gasoline, perhaps (6)
11Successful actor takes one step (5)
15Ten share one limousine, eventually (5)
20Non-glossy issue is incomplete (5)
21Trap a couple of lemmings in small stream (7)
22Fictional motel owner keeps son in stitches (6)
23Fancy éclair is more decorative, in a way (6)
25Workers from research facility hospital ward (5)
26Drove as well, and was in front (6)
27Hot New England housing locations on the rise (6)
28Reportedly trims fruit (5)
30Try true courage (5)
31Wild plums from hillsides outside of park (5)
33Detailed description of half-off specials (4)

Solution