Clearly he's seeing it like a melon and is cashing in.
Only Nathan Astle (16), Ross Taylor (11) and Stephen Fleming (8) have made more ODI centuries although considering his batting position for much of his career, it could be argued that five tons is a light return in 234 matches.
Yesterday he flew past 50 in 39 balls - slowcoach by comparison with his 19-ball effort in the opening ODI last Sunday - but he was measured in the sense that he didn't go hard at every delivery. Indeed 49 of his 99 balls were runless.
But balancing that were 12 fours and five sixes, and if he did go quiet occasionally, it didn't last long, either courtesy of thunderous blows which bruised the boundary fences, or cleared them, or with singles or hard-run twos.
McCullum entered the 70s slapping Jeevan Mendis for six over the long-on fielder, which suggested absolute self-belief, and knowledge of how short some of the boundaries are at Seddon Park, depending on the placement of the pitch.
The 80s arrived with a fierce slap over long off from Mendis. There was one more maximum, bouncing Sachithra off the top of the sightscreen shortly before his departure. It took a clever piece of bowling by Mendis to remove him, the ball held back a touch and a return catch was the result.
But with the World Cup nine games away after last night, McCullum looks to be in rare form. His timing with the cup in mind is certainly impressive.
New Zealand need the skipper firing. There are others in New Zealand's top six who'd wish they had a bit of McCullum's touch right now.
Players, rugby or cricket, like talking about work ons. There's no shortage of them at the moment for the batsmen. Like running between the wickets for a start.
Brendon McCullum's ODI centuries
• 166: v Ireland, Aberdeen, 2008
• 131: v Pakistan, Abu Dhabi, 2009
• 101: v Canada, Mumbai, 2011
• 119: v Zimbabwe, Napier, 2012
• 117: v Sri Lanka, Hamilton, 2014
ODI average: 30.67 from 234 games
Scoreboard
New Zealand v Sri Lanka2nd ODI, Seddon Park, Hamilton
New Zealand
M Guptill c A Mathews b N Kulasekara 10
B McCullum c & b J Mendis 117
T Latham c KC Sangakkara b RHerath 5
R Taylor c T Perera b R Herath 34
D Vettori run out (J Mendis) 7
C Anderson run out (A Mathews/K Sangakkara) 5
L Ronchi run out (T Dilshan/K Sangakkara) 0
N McCullum run out (M Jayawardene) 13
A Milne st K Sangakkara b S Senanayake 19
M Henry not out 20
T Boult c L Thirimanne b S Senanayake 13
Extras (lb 0, wd 5, nb 0) 5
-Total (for 10 wickets, 50.0 overs) 248
Fall: 1-35 (Guptill, 6.4), 2-73 (Latham, 12.6), 3-158 (B McCullum, 30.1), 4-171 (Vettori, 33.2), 5-183 (Taylor, 36.3), 6-183 (Ronchi, 36.5), 7-185 (Anderson, 37.6), 8-207 (N McCullum, 44.4), 9-222 (Milne, 47.1), 10-248 (Boult, 49.6)
Bowling: Kulasekara 8-0-40-1 (1w, Perera 4-0-41-0, Senanayake 10-0-55-2, Herath 10-0-36-2, Mendis 10-0-47-1 (3w, Dilshan 7-0-27-0, Mathews 1-0-2-0
Sri Lanka
D Karunaratne lbw b N McCullum 21
T Dilshan c Ronchi b Henry 116
K Sangakkara c Latham b Milne 38
M Jayawardene c Taylor b Henry 27
A Mathews not out 39
L Thirimanne not out 2
Extras (lb 5, wd 4, nb 0) 9
-Total (for 4 wickets, 47.4 overs) 252
Fall: 1-64 (Karunaratne, 12.5), 2-116 (Sangakkara, 22.5), 3-163 (Jayawardene, 31.5), 4-237 (Dilshan, 45.3)
Bowling: Boult 10-1-52-0, Henry 9.4-0-34-2 (1w), Milne 8-0-61-1 (1w), N McCullum 6-0-40-1, Vettori 10-1-40-0, Anderson 4-0-20-0
Sri Lanka won by 6 wickets