4066 Rentokil by Jago

Jago gave us a tricky puzzle for Boxing Daywith DLM clues allowing a festive theme in the clues. The theme of the puzzle could be discerned from the unclued entries. These were HUNTING THE BIRD and ON THE FEAST OF STEPHEN. Brewers explains that St. Stephen’s Day, the 26 December was also called Wrenning Day, so called because it was a local custom among villagers to stone a wren to death on that day in commemoration of the stoning of St. Stephen. The title sounds like WREN TO KILL and the unclued 15 across is TROGLODYTES, the wren genus.

The solver then had to find the instructions given in the set of clues. This was given in the initial letters of clues, FOLD GRID TO ORIGAMIBIRD SO ONE IS HEAD. SEE WING. There are a number of ways of folding an origami bird, but in one form it is possible to highlight the word WREN under the wing, in which the M of SMASHED, turned 90 degrees acts the E and the Z of ZION, similarly turned acts as the N.

Definitions and letter mixtures are underlined.

Across
1 Feast and sup: Yuletide carousal (4)
UPSY
5 Out of one's skull from the brandy in the puds - shame! (7)
SMASHED
11 Levity from cracker well below par - "Knock, knock ..." (5)
PRANK
13 Drunkenly, I would fall and cut head ... (5)
CHUTE
14 ... going: "I'm Pope, I live in Vatican City!" So ... (7)
POMPEII
17 ... red vino meant I was giving a title to myself (12)
DENOMINATIVE
20 I'm so glad I got this thingumajig for Xmas (5)
GISMO
22 Dieting was no fun - let's cut the Xmas cake (4)
SAWN
25 There's a point to this: have a pee early on Boxing Day (4)
EPÉE
26 One Xmas I got given a leg of mutton ... (5)
GIGOT
30 ... only I'd expected garlic pate - and it was off (11)
ANTICIPATED
37 Red, red Robin wandered along ... (5)
ERRED
38 ... it was alert and grasping some holly (5)
SPRAG (see SPRACK = alert)
39 "Grand," said I, with a note of contempt ... (7)
DISDAIN
40 ... "a holiday: now we can put our feet up" (4)
FETE
 
Down
1 Mum raised and fed pup on Xmas leftovers ... (5)
UPPED
2 ... it's a sore point, considering what's in most food (7)
PROTEIN
3 Both together for Xmas? (3) 
SAM
4 I keel over when keg's empty (4)
SKEG
5 Read that Epistle I got from "The Rock" (7)
SPILITE
6 Decreed a December week served as the ... (4)
ACED
7 ... Season of Goodwill: being trashy, one's really taken for a ride by it ... (4)
SHAY
9 ... oh, it hasn't been easy, since the early Christians decided on it (4)
ETHE
10 Orders set menu, including Xmas Pudding (7) 
DESSERT
12 No "zizzing" in Church after Xmas dinner ... (4)
ZION
16 ... enthusiasm for the catechism? Pooh! ... (5)
OOMPH
18 ... I gave the epitome of grimace, being seen to ... (3)
MOE
19 ... screw up my face: "It's two ... (5)
TWIST
20 ... hours! Any danger of a drink?" I complained (7)
GROANED
21 Elap and Sabre (amongst many others) may have Xmas Trees stored in the attic (7)
SETTERS (ref. crossword setters for the Listener)
23 A stove for cooking festive saag aloo? (3)
AGA
24 Donations go toward animal charities at Xmas (7)
WOODRAT
28 Song about snowdrift: it is seasonal (4)
FITT
29 Eventually fed guests with sweet (5)
FUDGE
31 Eaten with sushi - or nibbled on Boxing Day? (4)
NORI
32 Winter always got very cold, I decided (4)
ICED
33 It completes the score in a docudrama about Jesus (4)
CODA
34 Nasty, ancient letter from Caesars ... (4)
AESC
36 ... giving their anger against Christians (3)
IRE