Originally Posted by
FlapJackMuncher
I heard that the Russian dog-bombs probably failed because they were trained to crawl under tanks successfully.
But, the training was done with Russian tanks which make a different noise (Russian engines) to German tanks (German engines) so when released they turned around and ran back towards the tanks that made the noise they'd been trained for.
According to
this source, Russian tanks used diesel, while German tanks used petrol. Unsurprisingly the dogs knew the difference and failed the first time they were tried in combat. But they went on to successfully destroy 304 German tanks.