AS Ukrainian tanks and infantry poured over the Russian border last week in a shock turn of the war, one serviceman revelled in a key Russian failing.
Unlike the troops that crashed into intricate Russian defensive lines that thwarted a large-scale offensive last year, the forces attacking the Kremlin's frontier crossed quickly and easily.
"They didn't protect the border. They only had anti-personnel mines scattered around trees at the side of the road and a few mines that they managed to quickly throw along the highways," said the serviceman, who identified himself as Ruzhyk.
Kyiv says it has thrown thousands of troops at Russia's Kursk region in the lightning operation that caught the Kremlin off guard and has seen Ukrainian forces capture more than two dozen Russian towns and villages.
Moscow has dispatched reinforcements to threatened frontier territories and evacuated tens of thousands of residents.
President Vladimir Putin has vowed retribution and said the incursion was evidence that Russia was at war with the West.
The speed of Ukraine's offensive — the largest by a foreign army inside Russia since World War 2 — contrasts starkly with grinding battles for individual cities that have defined Russia's invasion now in its third year.
"We have another example when Russian complacency prevailed," Ukrainian military analyst Mykola Bielieskov said.
"Russia assumed that since it had initiative elsewhere, Ukraine wouldn't dare to do things we've seen," he said, referring to months of incremental Russian advances along the front.
While the offensive has injected Ukrainian troops with a much-needed morale boost, it has also raised questions about how Russia will respond. Both Moscow and Kyiv have been tight-lipped about the scope and character of the fighting in Kursk.
Slinging rucksacks and assault rifles over their shoulders before crossing back into Russia, one 27-year-old squad leader, who identified himself as Faraon, was sparing but direct in his description of battles in Kursk.
"I saw a lot of death in the first few days. It was terrifying at first but then we got used to it," he said.
"There have been many deaths," he repeated next to a forest road leading to the frontier, without elaborating.
In a leafy clearing where Ukrainian tank crews were preparing to deploy to Kursk, a commander described the operation as a morale boost for an army suffering manpower and weapons shortages.
"There have been no significant victories in Ukraine in recent months. Only the Russians were advancing," he explained.
He said the assault was de facto a win for Ukraine because it would force the Kremlin to reinforce other weak border regions with troops that could then not be deployed to Ukraine.
"If they keep some grouping of forces in Kursk that they can't use (in Ukraine) then it's already a success. Let's see how it develops," he added.
Ruzhyk, 21, in a black T-shirt and camouflaged trousers, echoed the sentiment that the Ukrainian push had placed Moscow in a bind.
"If they start moving troops from the other side of the border then they won't be able to hold the line there," he said.
A senior Ukrainian official however earlier said that Russian attacks in the eastern Donetsk region — a long-sought prize for Putin — had not let up.
And the Institute for the Study of War, a United States-based research group, noted that Russian forces had continued their gains unabated in the industrial territory over recent days.
Several soldiers said Russia was dropping a huge number of glide bombs to fend off the assault, testimony echoed by civilian evacuees over recent days.
Asked whether Russia was flying drones — now omnipresent over the battlefield in Donetsk — in Kursk, one tank crew member hoisted himself down by the gun barrel before answering.
"It's totally quiet," the 30-year-old said moments before a barrage of Ukrainian-launched rockets traced lines in the sky above a field of blooming sunflowers.
What exactly Ukraine's end game with the Kursk operation is remains an open question.
Whether Ukraine can hold the territory depends partly on whether Russia attempts to reclaim it or entrenches to halt further advances, said Bielieskov, the analyst.
"I see no reason that Ukraine can't extract a high price from Russia if they try to reclaim these territories," he said.
The writers are from AFP