The Blob
Teenagers Steve and Jane are loitering in a Lover's Lane. They see an object in the night sky crash-land nearby. They investigate. It is The Blob, a jelly-like thing from Outer Space that consumes flesh.  It kills an old man, a doctor, and a nurse. It doubles in size after each feeding. Steve and Jane report their findings to the police. They are dismissed as crazy teenagers. In the meantime, The Blob has consumed many others.