The Day of Pentecost is typically associated with stupendous signs and miracles. Because of brief descriptions given in Acts 2, various religious denominations have sprung up which practice speaking in gibberish--which the disciples definitely were not doing--and being "slain in the Spirit", which is clearly not a biblical concept. What one will see is that these sincere but misled people focus on miracles and manifestations as "proof" that they have received the Holy Spirit.