This, he says, will at least disprove one particularly malign piece of Kremlin disinformation about the enemy that held him captive in the bunker of Grozny's presidential palace for two weeks - that Chechen fighters are castrating Russian prisoners: "If you want, I can show you this is not true."
The offer to remove his trousers is declined. But the result is the same: yet another rout for Russia in an escalating propaganda war that, in the end, may prove as decisive, at least politically, as the real, and scarcely less disastrous, war in the mudand snow of the northern Caucasus.
Captain Mychko, 31, was taken prisoner in Grozny after being wounded in a botched Russian assault on the centre of the Chechen capital on New Year's eve. Along with half a dozen other prisoners whose mothers trekked to Grozny to search for their missing sons, he this week made it back to Moscow.
Not only did the Chechens not castrate him, Captain Mychko told his audience at an anti-war meeting in Moscow, they probably saved his life, dragging him from the flaming wreck of his armoured personnel carrier after it had been hit by a rocket-propelle d grenade near Freedom Square in the centre of Grozny.
Scores, possibly hundreds, of Russian prisoners remain in Chechen hands, some of them in the ravaged presidential palace, others in remote villages and makeshift prisons outside the city.
The release of Captain Mychko and a handful of others, though, highlights just how badly President Boris Yeltsin and his narrow circle of aides have misjudged their enemy. Chechnya has not only proved its skill at combat in five weeks of war against Europe's biggest army, but also its mastery of the much more subtle form of combat called propaganda.
Presenting the newly released prisoners to a meeting of soldiers' mothers in Moscow, Viktor Poptsov, a Russian anti-war activist who travelled to Grozny to help secure their release, explained the strategy: "Our goal is to expose the lies that surround the Russian army in Chechnya and to understand the real nature of this operation to disarm so-called armed bandit formations."
Authorities in Moscow describe Chechen fighters as a band of bloodthirsty gangsters and, when forced to admit setbacks, attribute their tenacity to the fanaticism of Islamic mercenaries, Ukrainian fascists and, in one particularly far-fetched report, female snipers in white stockings from Lithuania.
Chechnya's devastatingly effective response to such stories has been the testimony of Russia's own soldiers.All say they were well treated in captivity and are horrified by the carnage and chaos they encountered during what they had been told was an operation to "restore constitutional law and order".
Maxim Yashinko, a tank driver from the Kantemirov Division, says he was ordered into Grozny on New Year's eve without even a map, without any clear orders and without any real preparation. His unit's first clash that night took place just inside the citylimits. It lasted about 40 minutes and left the road littered with six burnt-out armoured vehicles.
Only when it was over did he realise the full horror of what had happened: "We were fighting with the Ministry of Interior troops, not the Chechens. We had destroyed all their equipment and killed our own men." He says he never really knew who or where the enemy was until the Chechens took him prisoner.
Also captured in the New Year's assault was Yuri Koptsov, a 37-year-old lieutenant-colonel and, unlike most of the troops sent to Chechnya, a professional soldier rather than a conscript. "We did not storm the capital but just threw ourselves into a stupid, unplanned attack. No one knew what they were supposed to be doing." He too had no map.
But it was not until the end of his first week in the bunker of the presidential palace, he says, that he realised the extent of incompetence and self-delusion surrounding the entire venture. He was given a copy of the official Russian government newspaper, Rossiskaya Gazeta, and read a report purporting to describe the situation in Grozny. The city, the paper said, had fallen and was now under Russian control. "It was pure fantasy. How can you fight a war like this?''