In the game contra, what does the capsule with a b do?

The capsule with a B makes you invincible for a short time.   The Barrier (B), also known as Barrier Shield or Force Field, is a power-up that first appears in the third level of the original Contra. It is a special power-up that makes the affected player have temporary invincibility. The player will flash red and blue, and any enemies that make contact with them will be destroyed instantly. 

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