In use, the blocks may be stacked to provide {HEAD ~ an interlocking structure} wherein the protrusions of one block interfit within {TAIL ~ the insets} of another block 
In use , the blocks may be stacked to provide { HEAD ~ an interlocking structure } wherein the protrusions of one block interfit within { TAIL ~ the insets } of another block
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH