There are certain spots in the game (not just on this stage; activating the train's levers in Mission 3, and Mission 6's wavy bridge also does this, for example) where the character will do their alternate melee attack; the males kick while standing up and use a punching glove when crouching, and Eri will do some pretty cool kicks, while Fio will push the enemies with her arms. These alternate melee hits do the same damage as a regular melee (3HP), but prevent the character from moving, so it's a straight downgrade from a gameplay perspective. One way to avoid performing them is to melee the enemies while in the air. I think, specifically for the PS1 port of Metal Slug X, instead of replacing the standard knife attack, the males instead do the standing kick/crouching punch _in addition_ to the standard knife melee, resulting in double damage on these specific alternate melee spots. Starting from Metal Slug 6, these alternate melee attacks can be manually performed by holding the Special button and then pressing the Attack button.

@@XSquareStickIt ah thank you, tho what I meant specifically was what triggers the game to switch animation, like is it enemy-dependent, coordinate-dependent...?

@@shinkiro403 It just happens at specific places, like most of Mission 2-3, kicking the train's lever in Mission 3, and the wavy bridge at Mission 6-1.

This is because Venutians either killed or mind controlled humans to make them figth you, they had no other use for them, but Martians are different because Venusians EAT THEM, more than POWs, they were food waiting to be eaten