 The Dagobah set needed to be elevated to give Frank Oz (qv) and  three other puppeteers room to control the Yoda puppet from below.  For proper interaction, Mark Hamill (I) (qv) was given an earpiece  so he could hear Frank Oz doing Yodas voice. Mark Hamill reportedly  had a hard time concentrating on his dialogue, since his earpiece  occasionally picked up a radio frequency playing the Rolling Stones.