"Col1 Like '%Cu_%' " means that matches string with "everything before Cu followed by at least one character"
'_Cus' = matches because there is substring Cu followed by one character
'Cus_' = matches because there is substring Cu followed by more than one character
'C_us' = doesn't match, because there is no substring Cu
'Cus' = matches because there is substring Cu followed by one charac
'Cu_s' = matches because there is substring Cu followed by more than one character
Is it clear?