invisible ink

spy

Covert information gatherer

• covertIntentionally concealed
• clandestineConcealed from authorities
• secret messageCovert transmitted information

dead drop · tradecraft · cipher · encode · decipher · agent · intelligence · undercover · steganography · intercept

hidden

Kept out of sight

• unseenNot perceived visually
• imperceptibleCannot be sensed
• undetectableImpossible to notice

latent · disguise · camouflage · veil · obscure · transparent · disappearing · reveal · cloak · mask

lemon juice

Pressed citrus liquid

• ultravioletWavelengths shorter than violet
• UV lightInvisible solar radiation
• oxidationLosing electrons chemically

acid · milk · vinegar · baking soda · phenolphthalein · reagent · developer · blacklight · chemical reaction · heat source

watermark

Translucent authentication mark

• authenticationConfirming genuine identity
• tamper-evidentShows if opened
• fraud preventionStopping dishonest financial activity

counterfeit · encryption · document security · forgery · banknote · currency · passport · certificate · anti-counterfeiting · verification

magic trick

Performed feat seeming impossible

• children's gameStructured play for youth
• treasure huntGame seeking hidden prizes
• party favorSmall memento for guests

toy · puzzle · scavenger hunt · birthday party · decoder · secret diary · adventure · mystery game · escape room

• novelty itemswhoopee cushion, rubber chicken, fake vomit, hand buzzer, fake poop
• Steganographyhidden message, digital watermark, hidden text, microdot, payload
• codes and cipherscipher, code, decode, decrypt, encrypt
• childhood secretswhispering, secret diaries, pinky promise, secret notes, coded messages
• prankspranks, prank calls, prank call, prank video, practical jokes
• science experimentsvolcano model, elephant toothpaste, color change, slime making, baking soda volcano