Here is how you access 2 secret weapons:
don't fire a shot for 2 minutes since the beginning of a game and don't let aliens hurt you either
Shoot one alien with your one and first shot. walk to the corpse wait there untill the other aliens nearly killed you
Run around without shooting or getting hit for 65 seconds in game.
Complete Game On Hardcore Difficulty
Blade Gun (Secret Weapon):
Enter Survival Mode. With your first shot, kill an enemy thing.
If your first shot doesn't kill it, quit and start all over again.
Wherever the bullet impacted the creature, stand on that. It'll be somewhere in the middle of the blood/corpse. Wait until creatures take you below 1/5 of your health, without moving. Without moving, kill all the creatures that were attacking you. If successful, you will receive the Blade Gun immediatley.
Alien Zoo Keeper Mini Game:
Start viewing the credits of the game. Click every line that has the letter 'o' in it. You will hear a chiming noise to confirm
that you clicked it correctly. Click every line with a letter 'o'
in it. Then when the list of names end, wait a while and more
should come up. Click those with an 'o' in them as well and the words 'Secrets' should appear. Click it and you should be able to play the mini game. Make sure you click all of them with the 'o' or it will not work.