( ( When ( you get ) ) ( ( ( ( goosebumps ( a ( small muscle ) ) ) ( at ( ( the base ) ( of ( a ( hair contracts ) ) ) ) ) ) ( to ( ( cause ( the hair ) ) ( to stand-on-ends ) ) ) ) . ) )
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (PRP you)) (VP (VBP get)))) (VP (VBZ goosebumps) (NP (DT a) (JJ small) (NN muscle)) (PP (IN at) (NP (NP (DT the) (NN base)) (PP (IN of) (NP (DT a) (NN hair) (NNS contracts))))) (S (VP (TO to) (VP (VB cause) (NP (DT the) (NN hair)) (PP (TO to) (NP (NNS stand-on-ends))))))) (. .)))
When you get goosebumps a small muscle at the base of a hair contracts to cause the hair to stand-on-ends .
(ROOT (S (NP (NNS Goosebumps)) (VP (VBP happen) (PRN (-LRB- -LRB-) (VB s) (-RRB- -RRB-)) (SBAR (WHADVP (WRB when)) (S (NP (NNS mammals)) (VP (VB raise) (NP (PRP$ their) (NN hair)) (PP (IN with) (NP (NP (JJ tiny) (NNS muscles)) (PP (IN in) (NP (DT the) (NN skin))))))))) (. .)))
Goosebumps happen(s) when mammals raise their hair with tiny muscles in the skin.